Search

Purpose Adolescent and young adult cancer survivors require lifelong healthcare to address the late effects of therapy. We examined the impact of different provider models of long‐term follow‐up (LTFU) care on adherence to recommended surveillance. Methods We conducted a retrospective cohort study using administrative health databases in Ontario, Canada. Five‐year survivors were identified from IMPACT, a database of patients aged 15–20.9 years at diagnosis of six cancers between 1992 and 2010. We defined three models of LTFU care hierarchically: specialized survivor clinics (SCCs), general cancer clinics (GCCs), and family physician (FP). We assessed adherence to the Children's Oncology Group surveillance guidelines for cardiomyopathy and breast cancer. Multistate models assessed adherence transitions and impacts of LTFU attendance. Results A total of 1574 survivors were followed for a mean of 9.2 years (range 4.3–13.9 years) from index (5‐year survival). The highest level of LTFU attended in the first 2‐years post‐index was a GCC (47%); only 16.7% attended a SCC. By the end of study, 72% no longer attended any of the models of care and only 2% still attended an SCC. Among 188 survivors requiring breast cancer surveillance, 6.9% were adherent to their first required surveillance testing. Attendance at a SCC in the previous year and higher cumulative FP or GCC visits increased the rate of subsequently becoming adherent. Among 857 survivors requiring cardiomyopathy surveillance, 11% were adherent at study entry. Each subsequent SCC visit led to an 11.3% (95% CI: 1.05–1.18) increase in the rate of becoming adherent. Conclusion LTFU attendance and surveillance adherence are sub‐optimal. SCC follow‐up is associated with greater adherence, but few survivors receive such care, and this proportion diminished over time. Interventions are needed to improve LTFU attendance and promote surveillance adherence., Long‐term follow‐up care attendance and surveillance adherence are sub‐optimal among adolescent and young adult cancer survivors. Specialized survivor clinic follow‐up is associated with greater adherence, but few survivors receive such care, and this proportion diminished over time. Interventions are needed to improve the long‐term follow‐up care attendance and promote surveillance adherence.

Background High-quality estimates of health care costs are required to understand the burden of illness and to inform economic models. We estimated the costs associated with hepatitis C virus (HCV) infection from the public payer perspective in Ontario, Canada. Methods In this population-based retrospective cohort study, we identified patients aged 18-105 years diagnosed with chronic HCV infection in Ontario from 2003 to 2014 using linked administrative data. We allocated the time from diagnosis until death or the end of follow-up (Dec. 31, 2016) to 9 mutually exclusive health states using validated algorithms: no cirrhosis, no cirrhosis (RNA negative) (i.e., cured HCV infection), compensated cirrhosis, decompensated cirrhosis, hepatocellular carcinoma, both decompensated cirrhosis and hepatocellular carcinoma, liver transplantation, terminal (liver-related) and terminal (non-liver-related). We estimated direct medical costs (in 2018 Canadian dollars) per 30 days per health state and used regression models to identify predictors of the costs. Results We identified 48 239 patients with chronic hepatitis C, of whom 30 763 (63.8%) were men and 35 891 (74.4%) were aged 30-59 years at diagnosis. The mean 30-day costs were $798 (95% confidence interval [CI] $780-$816) (n = 43 568) for no cirrhosis, $661 (95% CI $630-$692) (n = 6422) for no cirrhosis (RNA negative), $1487 (95% CI $1375-$1599) (n = 4970) for compensated cirrhosis, $3659 (95% CI $3279-$4039) (n = 3151) for decompensated cirrhosis, $4238 (95% CI $3480-$4996) (n = 550) for hepatocellular carcinoma, $8753 (95% CI $7130-$10 377) (n = 485) for both decompensated cirrhosis and hepatocellular carcinoma, $4539 (95% CI $3746-$5333) (n = 372) for liver transplantation, $11 202 (95% CI $10 645-$11 760) (n = 3201) for terminal (liver-related) and $8801 (95% CI $8331-$9271) (n = 5278) for terminal (non-liver-related) health states. Comorbidity was the most significant predictor of total costs for all health states. Interpretation Our findings suggest that the financial burden of HCV infection is substantially higher than previously estimated in Canada. Our comprehensive, up-to-date cost estimates for clinically defined health states of HCV infection should be useful for future economic evaluations related to this disorder.

Despite significant advances in cancer precision medicine, a significant hurdle to its broader adoption remains the multitude of variants of unknown significance identified by clinical tumor sequencing and the lack of biologically validated methods to distinguish between functional and benign variants. Here we used functional data on MAP2K1 and MAP2K2 mutations generated in real-time within a co-clinical trial framework to benchmark the predictive value of a three-part in silico methodology. Our computational approach to variant classification incorporated hotspot analysis, three-dimensional molecular dynamics simulation, and sequence paralogy. In silico prediction accurately distinguished functional from benign MAP2K1 and MAP2K2 mutants, yet drug sensitivity varied widely among activating mutant alleles. These results suggest that multifaceted in silico modeling can inform patient accrual to MEK/ERK inhibitor clinical trials, but computational methods need to be paired with laboratory- and clinic-based efforts designed to unravel variabilities in drug response. Significance: Leveraging prospective functional characterization of MEK1/2 mutants, it was found that hotspot analysis, molecular dynamics simulation, and sequence paralogy are complementary tools that can robustly prioritize variants for biologic, therapeutic, and clinical validation. See related commentary by Whitehead and Sebolt-Leopold, p. 4042

The mutation of K‐RAS represents one of the most frequent genetic alterations in cancer. Targeting of downstream effectors of RAS, including of MEK and ERK, has limited clinical success in cancer patients with K‐RAS mutations. The reduced sensitivity of K‐RAS‐mutated cells to certain MEK inhibitors (MEKi) is associated with the feedback phosphorylation of MEK by C‐RAF and with the reactivation of mitogen‐activated protein kinase (MAPK) signaling. Here, we report that the RAF dimer inhibitors lifirafenib (BGB‐283) and compound C show a strong synergistic effect with MEKi, including mirdametinib (PD‐0325901) and selumetinib, in suppressing the proliferation of K‐RAS‐mutated non‐small‐cell lung cancer and colorectal cancer (CRC) cell lines. This synergistic effect was not observed with the B‐RAFV600E selective inhibitor vemurafenib. Our mechanistic analysis revealed that RAF dimer inhibition suppresses RAF‐dependent MEK reactivation and leads to the sustained inhibition of MAPK signaling in K‐RAS‐mutated cells. This synergistic effect was also observed in several K‐RAS mutant mouse xenograft models. A pharmacodynamic analysis supported a role for the synergistic phospho‐ERK blockade in enhancing the antitumor activity observed in the K‐RAS mutant models. These findings support a vertical inhibition strategy in which RAF dimer and MEKi are combined to target K‐RAS‐mutated cancers, and have led to a Phase 1b/2 combination therapy study of lifirafenib and mirdametinib in solid tumor patients with K‐RAS mutations and other MAPK pathway aberrations., The reduced sensitivity of K‐RAS‐mutated cancer cells to MEK inhibitors (MEKi), such as selumetinib and mirdametinib, is associated with feedback phosphorylation of MEK by upstream RAF reactivation. RAF dimer inhibitors, such as lifirafenib and compound C, in combination with MEKi potently suppress RAF‐dependent MEK phosphorylation and lead to sustained inhibition of MAPK signaling and tumor growth.

Background Because of high smoking rates and HIV-related factors, people with HIV may be at high risk for chronic obstructive pulmonary disease (COPD); however, population-based estimates of the incidence of COPD among people with HIV are lacking, particularly for women. We compared the incidence of COPD among Ontario adults aged 35 years or more with and without HIV between Jan. 1, 1996, and Dec. 31, 2015. Methods We conducted a population-based study using Ontario's health administrative databases. We compared the incidence of COPD between people with and without HIV using standardized incidence ratios and generalized estimating equations with a log link function. Results We identified 1849 people with HIV and 1 168 727 HIV-negative people who were newly diagnosed with COPD between 1996 and 2015. People with HIV were younger than HIV-negative people (mean age 49.7 [standard deviation 10.4] yr v. 62.2 [standard deviation 14.8] yr; standardized difference 0.98). Rates of COPD were higher among people with HIV than among HIV-negative people (10.4 v. 9.0 cases per 1000 person-years; standardized incidence ratio 1.16, 95% confidence interval [CI] 1.10 to 1.21; adjusted rate ratio 1.34, 95% CI 1.27 to 1.41). In sex-stratified analyses, rates of COPD were higher among men with HIV (adjusted rate ratio 1.32, 95% CI 1.24 to 1.40) and women with HIV (adjusted rate ratio 1.54, 95% CI 1.37 to 1.72) than among men and women without HIV. In a sensitivity analysis, smoking explained observed differences in COPD incidence. Interpretation People with HIV had higher rates of incident COPD than HIV-negative people. This may reflect the disproportionately higher prevalence of smoking among the former.

RATIONALE: Despite its importance as a leading risk factor for chronic obstructive pulmonary disease (COPD), there is a minimal amount of population-level information regarding smoking prevalence a...

Purpose: While mutations in BRAF in metastatic colorectal cancer (mCRC) most commonly occur at the V600 amino acid, with the advent of next-generation sequencing, non-V600 BRAF mutations are increasingly identified in clinical practice. It is unclear whether these mutants, like BRAF V600E, confer resistance to anti-EGFR therapy. Experimental Design: We conducted a multicenter pooled analysis of consecutive patients with non-V600 BRAF-mutated mCRCs identified between 2010 and 2017. Non-V600 BRAF mutations were divided into functional classes based on signaling mechanism and kinase activity: activating and RAS-independent (class 2) or kinase-impaired and RAS-dependent (class 3). Results: Forty patients with oncogenic non-V600 BRAF–mutant mCRC received anti-EGFR antibody treatment [n = 12 (30%) class 2 and n = 28 (70%) class 3]. No significant differences in clinical characteristics were observed by mutation class. In contrast, while only 1 of 12 patients with class 2 BRAF mCRC responded, 14 of 28 patients with class 3 BRAF responded to anti-EGFR therapy (response rate, 8% and 50%, respectively, P = 0.02). Specifically, in first- or second-line, 1 of 6 (17%) patients with class 2 and 7 of 9 (78%) patients with class 3 BRAF mutants responded (P = 0.04). In third- or later-line, none of 6 patients with class 2 and 7 of 19 (37%) patients with class 3 BRAF mutants responded (P = 0.14). Conclusions: Response to EGFR antibody treatment in mCRCs with class 2 BRAF mutants is rare, while a large portion of CRCs with class 3 BRAF mutants respond. Patients with colorectal cancer with class 3 BRAF mutations should be considered for anti-EGFR antibody treatment. See related commentary by Fontana and Valeri, p. 6896

Over 300 BRAF missense mutations have been identified in patients, yet currently approved drugs target V600 mutants alone. Moreover, acquired resistance inevitably emerges, primarily due to RAF lesions that prevent inhibition of BRAF V600 with current treatments. Therefore, there is a need for new therapies that target other mechanisms of activated BRAF. In this study, we use the Proteolysis Targeting Chimera (PROTAC) technology, which promotes ubiquitination and degradation of neo-substrates, to address the limitations of BRAF inhibitor-based therapies. Using vemurafenib-based PROTACs, we achieve low nanomolar degradation of all classes of BRAF mutants, but spare degradation of WT RAF family members. Our lead PROTAC outperforms vemurafenib in inhibiting cancer cell growth and shows in vivo efficacy in a Class 2 BRAF xenograft model. Mechanistic studies reveal that BRAFWT is spared due to weak ternary complex formation in cells owing to its quiescent inactivated conformation, and activation of BRAFWT sensitizes it to degradation. This study highlights the degree of selectivity achievable with degradation-based approaches by targeting mutant BRAF-driven cancers while sparing BRAFWT, providing an anti-tumor drug modality that expands the therapeutic window., Hundreds of BRAF mutations have been identified in patients with cancer but currently approved drugs only target BRAF V600 mutants. Here, the authors develop a vemurafenib-based PROTAC that induces degradation of all classes of BRAF mutants without affecting wild-type RAF proteins.

To improve the long-term outcomes of high tibial osteotomy (HTO) for gonarthritis, many cartilage repair procedures appeared, but their effects were controversial. To evaluate the efficacy of cartilage repair procedures during HTO for gonarthritis, we performed this update meta-analysis. We performed the system retrieval for clinical trials using various databases and then pooled the outcomes of the included studies. Fifteen studies were involved. The pooled results indicated that there were no significant differences in Kellgren and Lawrence (KL) scale (mean difference [MD] = 0.02, 95% confidence interval [CI] = −0.01 to 0.06, p = 0.24), the femorotibial angle (MD = 0.06, 95% CI = −0.04 to 0.16, p = 0.22), and magnetic resonance imaging (MRI) outcomes (MD = 12.53, 95% CI = −2.26 to 27.32, p = 0.10) of patients in experimental group than control. The subgroup analysis showed that the clinical outcomes of abrasion arthroplasty (AA) were worse than control group (standardized mean difference [SMD] −2.65, 95% CI = −3.67 to −1.63, p

BACKGROUND: The risk of death in people after their first admission to hospital or first presentation to the emergency department for any reason is not known. The objective of this study was to estimate the risk of death among older adults who had had no admissions to hospital or emergency department visits in the preceding 5 years. METHODS: We used administrative data from Ontario, Canada, from 2007 to 2017 to measure the 5-year risk of death in community-dwelling adults aged 66 years and older after their first planned or unplanned hospital admission or emergency department visit, and among those who were neither admitted to hospital nor presented to the emergency department. We describe how this risk varied by age. RESULTS: Among 922 074 community-dwelling older adults, 12.7% died (116 940 deaths) over a follow-up of 3 112 528 person-years (standardized mortality rate 53.8 per 1000 person-years). After the first unplanned hospital admission, 39.7% died (59 234 deaths, standardized mortality rate 127.6 per 1000 person-years). After the first planned hospital admission, 13.0% died (10 775 deaths, standardized mortality rate 44.6 per 1000 person-years). After the first visit to the emergency department, 10.9% died (35 663 deaths, standardized mortality rate 36.2 per 1000 person-years). Among those with neither an emergency department visit nor hospital admission during follow-up, 3.1% died (11 268 deaths, standardized mortality rate 29.6 per 1000 person-years). Slightly more than half of all deaths were in those with first unplanned hospital admission (50.7%). INTERPRETATION: Death within 5 years of first unplanned hospital admission for older adults is frequent and common. Knowledge of this risk may influence counselling and patient preferences and may be useful in research and analyses for health system planning.

BRAF V600E colorectal cancers are insensitive to RAF inhibitor monotherapy due to feedback reactivation of receptor tyrosine kinase signaling. Combined RAF and EGFR inhibition exerts a therapeutic effect, but resistance invariably develops through undefined mechanisms. In this study, we determined that colorectal cancer progression specimens invariably harbored lesions in elements of the RAS–RAF–MEK–ERK pathway. Genetic amplification of wild-type RAS was a recurrent mechanism of resistance in colorectal cancer patients that was not seen in similarly resistant melanomas. We show that wild-type RAS amplification increases receptor tyrosine kinase-dependent activation of RAS more potently in colorectal cancer than in melanoma and causes resistance only in the former. Currently approved RAF inhibitors inhibit RAF monomers but not dimers. All the drug-resistant lesions we identified activate BRAF V600E dimerization directly or by elevating RAS-GTP. Overall, our results show that mechanisms of resistance converge on formation of RAF dimers and that inhibiting EGFR and RAF dimers can effectively suppress ERK-driven growth of resistant colorectal cancer. Cancer Res; 77(23); 6513–23. ©2017 AACR.

The initiating oncogenic event in almost half of human lung adenocarcinomas is still unknown, a fact that complicates the development of selective targeted therapies. Yet these tumours harbour a number of alterations without obvious oncogenic function including BRAF-inactivating mutations. Inactivating BRAF mutants in lung predominate over the activating V600E mutant that is frequently observed in other tumour types. Here we demonstrate that the expression of an endogenous Braf(D631A) kinase-inactive isoform in mice (corresponding to the human BRAF(D594A) mutation) triggers lung adenocarcinoma in vivo, indicating that BRAF-inactivating mutations are initiating events in lung oncogenesis. Moreover, inactivating BRAF mutations have also been identified in a subset of KRAS-driven human lung tumours. Co-expression of Kras(G12V) and Braf(D631A) in mouse lung cells markedly enhances tumour initiation, a phenomenon mediated by Craf kinase activity, and effectively accelerates tumour progression when activated in advanced lung adenocarcinomas. We also report a key role for the wild-type Braf kinase in sustaining Kras(G12V)/Braf(D631A)-driven tumours. Ablation of the wild-type Braf allele prevents the development of lung adenocarcinoma by inducing a further increase in MAPK signalling that results in oncogenic toxicity; this effect can be abolished by pharmacological inhibition of Mek to restore tumour growth. However, the loss of wild-type Braf also induces transdifferentiation of club cells, which leads to the rapid development of lethal intrabronchiolar lesions. These observations indicate that the signal intensity of the MAPK pathway is a critical determinant not only in tumour development, but also in dictating the nature of the cancer-initiating cell and ultimately the resulting tumour phenotype.

Synthetic oral cannabinoids (nabilone and dronabinol) may have adverse respiratory effects. Our purpose was to describe the scope, pattern, and patient characteristics associated with incident off-label synthetic oral cannabinoid use among older adults with chronic obstructive pulmonary disease (COPD) compared to older adults without COPD. This was a retrospective, population-based, cohort study using Ontario, Canada, heath administrative data. Individuals aged 66 years or older were included, and physician-diagnosed COPD was identified using a previously validated, highly specific algorithm. Incident off-label oral cannabinoid use was examined between April 1, 2005 and March 31, 2015. Descriptive statistics were used to describe drug use patterns. Multiple logistic regression was used to identify patient characteristics associated with incident drug use. There were 172,282 older adults with COPD and 1,068,256 older adults without COPD identified between April 1, 2005 and March 31, 2015. Incident synthetic oral cannabinoid use during this period occurred with significantly greater (p

The use of hypofractionated radiotherapy (HFRT) in patients with breast cancer and ductal carcinoma in situ (DCIS) in Ontario, Canada, from 2009 to 2015 was reported. A retrospective cohort study was conducted using data from the Institute for Clinical Evaluative Sciences (ICES). Patients with a breast cancer or DCIS diagnosis between 2009 and 2015 who received adjuvant breast or chest wall radiation were included. Trends in HFRT use (≤16 fractions) and factors associated with HFRT use in a multivariable logistic regression model with physician-level random effect were reported. The approximate number of hours that could be saved if all patients were to receive HFRT was calculated. A total of 42 072 patients were included. All included characteristics were significantly associated with HFRT use. Hypofractionated radiotherapy use in patients with breast cancer and DCIS increased to around 75% in 2015. In stage I/II patients with mastectomy and chest wall radiation, HFRT use increased to 40% in 2015. Hypofractionated radiotherapy use in patients with regional nodal radiation or reconstruction has increased but remains under 20%. For breast cancer patients with breast-conserving surgery (BCS) and breast radiation, 56 265 visits corresponding to 7200 hours of treatment or 3500 additional HFRT courses could have been saved. In conclusion, HFRT use in Ontario has increased in all patient populations but is nonuniform among physicians and institutions. Use of HFRT in chest wall and regional nodal radiation remains relatively lower than in breast cancer and DCIS patients with BCS.

K-RAS mutation represents one of the most frequent genetic alterations in cancers. Monotherapy approaches targeting RAS downstream effectors such as MEK and ERK have had limited clinical success in patients with K-RAS-mutated cancers. The reduced sensitivity of K-RAS-mutated cells to certain MEK inhibitors is associated with feedback phosphorylation of MEK and reactivation of mitogen-activated protein kinase (MAPK) signaling. Herein, we report that RAF dimer inhibitor lifirafenib (BGB-283) shows strong synergistic effect with MEK inhibitor mirdametinib (PD-0325901) in suppressing proliferation of K-RAS-mutated cancer cell lines. This synergistic effect was not observed using vemurafenib, a first-generation B-RAFV600E selective inhibitor. Mechanistic analysis revealed that RAF dimer inhibition could suppress RAF-dependent MEK reactivation and led to sustained inhibition of MAPK signaling in K-RAS-mutated cells. Furthermore, combination synergy was observed in K-RAS mutant xenograft models. Pharmacodynamic analysis supported the role of synergistic phospho-ERK blockade in enhancing the antitumor activity in the K-RAS mutant models. These findings support the rationale to combine a RAF dimer inhibitor and a MEK inhibitor to treat K-RAS-mutated cancers and led to the ongoing a Phase Ib/II clinical trial of lifirafenib and mirdametinib in patients with K-RAS mutations or other MAPK pathway aberrations (Clinical Trial ID: NCT03905148). Citation Format: Xi Yuan, Xinwen Zhang, Rong Du, Shing-Hu Cheung, Min Wei, Changyou Zhou, Lai Wang, Todd Shearer, Badreddin Edris, Mary Smith, Zhan Yao, Claire N. Thant, Neal Rosen, Lusong Luo. RAF dimer inhibitor lifirafenib enhances the antitumor activity of MEK inhibitor mirdametinib in RAS mutant tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6415.

Background Dutasteride is a potent inhibitor of 5-alpha reductase enzymes that reduces concentrations of dihydrotestosterone to a greater extent than finasteride. Whether this has adverse implications for bone health is unknown. We compared the risk of osteoporosis and fractures in older men treated with dutasteride or finasteride. Methods We conducted a population-based retrospective cohort study with high-dimensional propensity score matching of Ontario men aged 66 years or older who started treatment with dutasteride or finasteride between January 1, 2006 and December 31, 2012. The primary outcome was a diagnosis of osteoporosis within 2 years of treatment initiation. A secondary outcome was osteoporotic or fragility fractures. Results We studied 31,615 men treated with dutasteride and an equal number of men treated with finasteride. Dutasteride-treated patients had a lower incidence of osteoporosis than those receiving finasteride [2.2 versus 2.6 per 100 person years; hazard ratio (HR) 0.82; 95% confidence interval (CI) 0.72 to 0.93]. This effect was no longer statistically significant following adjustment for specialty of prescribing physician (HR 0.90; 95% CI 0.78 to 1.02)]. There was no differential risk of fractures with dutasteride (HR 1.04; 95% 0.86 to 1.25). Conclusions Despite differential effects on 5-alpha reductase, dutasteride is not associated with an increased risk of osteoporosis or fractures in older men relative to finasteride. These findings suggest that dutasteride does not adversely affect bone health. Electronic supplementary material The online version of this article (10.1186/s12891-018-2076-9) contains supplementary material, which is available to authorized users.

Objective:Although evidence suggests that treatment seeking for mental illness has increased over time, little is known about how the health system is meeting the increasing demand for services. We examined trends in physician-based mental health service use across multiple sectors.Method:In this population-based study, we used linked health-administrative databases to measure annual rates of mental health–related outpatient physician visits to family physicians and psychiatrists, emergency department visits, and hospitalizations in adults aged 16+ from 2006 to 2014. We examined absolute and relative changes in visit rates, number of patients, and frequency of visits per patient, and assessed temporal trends using linear regressions.Results:Among approximately 11 million Ontario adults, age- and sex-standardized rates of mental health–related outpatient physician visits declined from 604.8 to 565.5 per 1000 population over the study period ( Ptrend= 0.04). Over time, the rate of visits to family physicians/general practitioners remained stable ( Ptrend= 0.12); the number of individuals served decreased, but the number of visits per patient increased. The rate of visits to psychiatrists declined ( Ptrend< 0.001); the number of individuals served increased, but the number of visits per patient decreased. Concurrently, visit rates to emergency departments and hospitals increased (16.1 to 19.7, Ptrend< 0.001 and 5.6 to 6.0, Ptrend= 0.01, per 1000 population, respectively). Increases in acute care service use were greatest for anxiety and addictions.Conclusions:The increasing acute care service use coupled with the reduction in outpatient visits suggest, overall, an increase in demand for mental health care that is not being met in ambulatory care settings.

Background Public drug coverage for triptan medications varies across jurisdictions in Canada, which may lead to differences in usage patterns and patient risk for medication overuse headache. Methods We conducted a population-based, cross-sectional analysis of publicly funded triptan use in seven provinces across Canada from January 1, 2012 to December 31, 2012. All patients who had filled at least one prescription for a triptan during the study period were included. We defined quantity limits of 6, 12, and 18 triptan units per month to assess the prevalence of high volumes of triptan use, which may place patients at risk for medication overuse headaches, and compared this prevalence between provinces with different funding restrictions. Results We identified 14,085 publicly funded users of triptans in 2012 in the seven provinces studied, 82.5% of whom were aged less than 65 years (N = 11,631). The prevalence of triptan use ranged substantially by province, from 0.04% in Ontario to a maximum of 1.0% in Manitoba (P

The incidence of neonatal opioid withdrawal is increasing in both Canada and the United States. However, the degree to which the treatment of pain with opioids, rather than the misuse of prescription opioids or heroin, contributes to the prevalence of neonatal opioid withdrawal remains unknown.We conducted a retrospective, population-based, cross-sectional study between 1992 and 2011 in Ontario with 2 objectives. First, we determined the annual incidence of neonatal abstinence syndrome. Second, using data from a subset of women eligible for publicly funded prescription drugs, we determined what proportion of women who deliver an infant with neonatal abstinence syndrome were given a prescription for an opioid before and during pregnancy.The incidence of neonatal abstinence syndrome in Ontario increased 15-fold during the study period, from 0.28 per 1000 live births in 1992 to 4.29 per 1000 live births in 2011. During the final 5 years of the study, we identified 927 deliveries of infants with neonatal abstinence syndrome to mothers who were public drug plan beneficiaries. Of these mothers, 67% had received an opioid prescription in the 100 days preceding delivery, including 53.3% who received methadone, an increase from 28.6% in the interval spanning 1 to 2 years before delivery (p 0.001). Prescription for nonmethadone opioids decreased from 38% to 17% (p 0.001).The incidence of neonatal opioid withdrawal in Ontario has increased substantially over the last 20 years. Most of the women in this cohort who delivered an infant with neonatal abstinence syndrome had received a prescription for an opioid both before and during their pregnancy.

Purpose Valproic acid is an anticonvulsant that also inhibits histone deacetylase (HDAC), a property that could worsen pulmonary function in patients with chronic obstructive pulmonary disease (COPD). The clinical significance of this property is unknown. We therefore compared the risk of COPD exacerbation in older patients with COPD commencing treatment with either valproic acid or phenytoin, an anticonvulsant that does not affect HDAC. Methods We conducted a population-based retrospective cohort study of Ontario residents with COPD aged 66 years or older who started treatment with valproic acid or phenytoin between 1 April 1993 and 30 November 2012. The primary outcome was a hospital admission or emergency department visit for a COPD exacerbation within 240 days of drug initiation. A secondary outcome examined initiation of oral corticosteroids in the outpatient setting. Results During the study period, we identified 4596 COPD patients who commenced valproic acid and 8478 who commenced phenytoin. Following multivariable adjustment, valproic acid did not increase the risk of the primary outcome (adjusted hazard ratio 1.00, 95% confidence interval 0.79 to 1.26). Although valproic acid was associated with a lower risk of initiating oral corticosteroids in the first thirty days following commencement of anticonvulsant therapy (adjusted hazard ratio 0.32; 95% confidence interval 0.21 to 0.49), no difference was observed during subsequent follow-up. Conclusion Among older patients with COPD, treatment with valproic acid does not increase the risk of adverse pulmonary outcomes relative to phenytoin. These findings suggest that valproate-induced HDAC inhibition is of little clinical relevance in this context. ">© 2015 The Authors. Pharmacoepidemiology and Drug Safety Published by John Wiley & Sons Ltd.

Background Activating mutations or structural rearrangements in BRAF are identified in roughly 75% of all pediatric low-grade astrocytomas (PLGAs). However, first-generation RAF inhibitors approved for adult melanoma have poor blood-brain penetrance and are only effective on tumors that express the canonical BRAFV600E oncoprotein, which functions as a monomer. These drugs (type I antagonists that target the "DFG-in" conformation of the kinase) fail to block signaling via KIAA1549:BRAF, a truncation/fusion BRAF oncoprotein which functions as a dimer and is found in the most common form of PLGA. Methods A panel of small molecule RAF inhibitors (including type II inhibitors, targeting the "DFG-out" conformation of the kinase) was screened for drugs showing efficacy on murine models of PLGA and on authentic human PLGA cells expressing KIAA1549:BRAF. Results We identify a type II RAF inhibitor that serves as an equipotent antagonist of BRAFV600E, KIAA1549:BRAF, and other noncanonical BRAF oncoproteins that function as dimers. This drug (MLN2480, also known as TAK-580) has good brain penetrance and is active on authentic human PLGA cells in brain organotypic cultures. Conclusion MLN2480 may be an effective therapeutic for BRAF mutant pediatric astrocytomas.

Key Points Question Is it possible to predict which patients with cancer will require early acute care after starting systemic therapy? Findings In a cohort study, using population-based administrative databases in Ontario, Canada, a score was developed and validated to predict a visit to the emergency department or a hospitalization within the first 30 days after starting systemic therapy for cancer based on cancer type, systemic therapy regimen, previous emergency department visits, and age. Meaning The findings suggest that patients at high risk for use of acute care after starting systemic therapy for cancer can be identified using a simple score that is available at the point of care., Importance Emergency department visits and hospitalizations after starting systemic therapy for cancer are frequent, undesirable, and costly. A score to quantify the risk of needing acute care can inform decision-making and facilitate the development of preventive interventions. Objective To develop and validate a score to predict early use of acute care after initiating systemic therapy for cancer. Design, Setting, and Participants A retrospective population-based cohort study was conducted between July 1, 2014, and June 30, 2015. Patients with cancer were eligible if they started a new systemic therapy for cancer, regardless of line of therapy. A total of 12 162 patients in Southwestern Ontario, Canada, formed the development cohort and 15 845 patients in Northeastern Ontario formed the validation cohort. Data analysis was conducted from December 1, 2016, to August 10, 2019. Exposures The Prediction of Acute Care Use During Cancer Treatment (PROACCT) score was created based on logistic regression in the development cohort. Combinations of cancer type and regimens were grouped into quintiles based on risk of needing acute care. The score was assessed in the validation cohort. Main Outcomes and Measures At least 1 emergency department visit or hospitalization within 30 days after starting systemic therapy for cancer identified from administrative databases. Results Among the 12 162 patients in the development cohort, 6903 were women and 5259 were men (mean [SD] age, 62.9 [12.6] years); among the 15 845 patients in the validation cohort, 9025 were women and 6820 were men (mean [SD] age, 62.9 [12.6] years). Use of acute care occurred within 30 days after initiation of systemic therapy in 3039 patients (25.0%) in the development cohort and 4212 patients (26.6%) in the validation cohort. Three characteristics predicted early use of acute care and formed the PROACCT score: combination of cancer type and treatment regimen, age, and emergency department visits in the prior year (C statistic, 0.67; 95% CI, 0.66-0.69; P, This cohort study uses population-based administrative and clinical databases to develop and validate a score to predict early use of acute care after initiating systemic therapy for cancer.

ARAF, BRAF and CRAF protein kinases are RAS effectors required for activation of ERK signaling. ARAF has relatively modest kinase activity and its biological functions are largely unknown. Here, we show that ectopic expression of ARAF but not B- or CRAF, leads to induction of RAS activation in cells with WT RAS. This phenomenon requires the binding of ARAF to RAS but not its kinase activity. ARAF was found to reduce inactivation of RAS by antagonizing its binding to the major RAS-GAP NF1. By this mechanism, the abundance of ARAF in cells determines cellular RAS-GTP levels, the dynamics of RTK-induced RAS activation and the biological consequences of RAS signaling. We find that a certain expression level of ARAF is required for growth factors induced proliferating or neural differentiation in PC12 cells. In RTK-dependent tumor cells, knocking down of ARAF leads to a reduction of RAS-GTP, thus impairs RAS signaling and the tumor growth. Furthermore, by investigating the tumor samples from MSK patients who are diagnosed with progressing disease after EGFR inhibitor treatment, we find the up-regulation of ARAF (including the ARAF gene amplification) is associated with EGFR inhibitor resistance in the lung cancer patients. We confirmed in cell line and xenograft models that a 5-fold elevation of ARAF expression is sufficient to eliminate RAS inhibition by EGFR inhibition and to cause resistance. Resistance in these cells could be overcome by combining EGFR and SHP2 inhibitors. The latter prevents EGFR activation of RAS-GTP exchange and thus would be expected with weaking the effects of NF1 inhibition by ARAF. Taken together, our work shows that ARAF directly activates RAS by antagonizing its interaction with NF1 and thus affects the duration and cellular response of growth factor activation and sensitivity of tumors to pharmacological inhibition of RTK-RAS signaling. Citation Format: Wenjing Su, Rona Yaeger, Na Na, Jaclyn Hechtman, Viktoriya Paroder, Sandra Misale, Sae-Won Han, Omar I. Abdel-Wahab, Frank McCormick, Neal Rosen, Zhan Yao. ARAF activates RAS by antagonizing its interaction with NF1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-265.

The clinical significance of BRAF alterations in well-differentiated (WD) metastatic pancreatic neuroendocrine tumor (panNET) is unknown, but BRAF-mutated panNET could represent a subset characterized by an identifiable and clinically actionable driver. Following the identification of two patients with WD metastatic panNET whose tumors harbored BRAF mutations, we queried the MSK-IMPACT series of 80 patients with WD metastatic panNET for additional mutations in BRAF, and in other genes involved in RAS/ RTK/ PI3K signaling pathways. BRAF mutations were identified in six samples (7.5%): two tumors harbored V600E mutations, one tumor each expressed K601E, T599K, and T310I mutations, and one tumor expressed both G596D and E451K BRAF. Few additional actionable driver alterations were identified. To determine the ERK activating capability of four BRAF mutations not previously characterized, mutant constructs were tested in model systems. Biochemical characterization of BRAF mutations revealed both high and low activity mutants. Engineered cells expressing BRAF K601E and V600E were used for in vitro drug testing of RAF and MEK inhibitors currently in clinical use. BRAF K601E demonstrated reduced sensitivity to dabrafenib compared to BRAF V600E, but the combination of RAF plus MEK inhibition was effective in cells expressing this mutation. Herein, we describe the clinical course of a patient with BRAF K601E and a patient with BRAF V600E WD metastatic panNET, and the identification of four mutations in BRAF not previously characterized. The combined clinical and biochemical data support a potential role for RAF and MEK inhibitors, or a combination of these, in a selected panNET population.

Low-grade gliomas account for ~30% of primary central nervous system tumors arising in children. Although LGGs grow slowly, inoperable tumors can lead to morbidity and premature death. The most common oncogenic event observed in nearly 70% of cases of Pilocytic astrocytomas (PA) and diffuse leptomeningeal glioneuronal tumors (DLGT)—is a recurrent tandem duplication on chromosome 7. This complex rearrangement results in the fusion of BRAF C-Terminus comprising of the kinase domain with KIAA1549 N-Terminus, an uncharacterized gene. Apart from creating this fusion, the entire region between KIAA1549 and BRAF comprising of 17 protein coding genes is duplicated. Currently, there are no accurate preclinical models for KIAA1549-BRAF duplication which has hindered targeted therapy for this class of pediatric brain tumors. Although cDNA overexpression of KIAA1549-BRAF has been shown to activate the MAPK pathway, in vivo models overexpressing the fusion protein lack the physiological features of either PA or DLGT. Our hypothesis in this project is that generating the entire tandem duplication event in addition to the Kiaa1549-Braf fusion is necessary for modeling the patho-physiological characteristics of the pediatric brain tumors. We have employed CRISPR based somatic genome editing to generate the tandem duplication of Kiaa1549-Braf in p53-/- adult neural stem cells ex-vivo, which results in brain tumors predominantly growing in the subarachnoid/leptomeningeal space and displays histopathological features of human DLGT. Further, we have shown that the Kiaa1549-Braf driven tumor lines can be inhibited by next generation Braf dimer inhibitors. In summary, we have developed a new preclinical model for Kiaa1549-Braf driven brain cancer and demonstrated efficacy against a new preclinical Braf inhibitor.

Background Some evidence suggests that the direct renin inhibitor aliskiren may increase the risk of severe hyperkalemia, stroke, or acute kidney injury (AKI) when prescribed with angiotensin-converting enzyme inhibitors (ACEi's) or angiotensin-receptor blockers (ARBs). The extent to which concomitant treatment increases the risk of these outcomes in routine clinical practice is unknown. We addressed this issue with the use of administrative databases. Methods We established a cohort of Ontarians treated with an ACEi or an ARB. Within this cohort, we conducted 3 case-control studies. Cases were patients hospitalized with 1 of 3 outcomes (hyperkalemia, AKI, or stroke). In each analysis, we identified up to 5 matched control subjects for each case. Conditional logistic regression was used to examine the association between hospitalization for each outcome and the use of aliskiren in the preceding 60 days. Results Among 903,346 patients aged 66 years and older treated with an ACEi or ARB during the 28-month study period, we identified 4235 hospitalized with hyperkalemia, 18,231 hospitalized with AKI, and 8283 hospitalized with stroke. After extensive multivariable adjustment, aliskiren therapy was not associated with a significant increase in the risk of hospitalization for hyperkalemia, AKI, or stroke. We found similar results in stratified analyses of patients with and without a history of chronic kidney disease, diabetes, or heart failure. Conclusions Among community-dwelling patients aged 66 years and older receiving therapy with an ACEi or an ARB, aliskiren use was not associated with hospitalization for hyperkalemia, AKI, or stroke.

Background Intravenous acyclovir-induced acute kidney injury (AKI) from drug crystallization in the renal tubules is described in case reports, review articles, and drug prescribing manuals. Similarly, AKI from oral acyclovir is described in case reports, but the risk in routine practice is unknown. Study Design Retrospective population-based cohort study. Setting & Participants We studied a large cohort of older patients in Ontario, Canada, receiving new outpatient prescriptions from 1997 to 2011 for oral acyclovir or valacyclovir (which is metabolized to acyclovir). The comparison drug was famciclovir, an antiviral used for indications similar to acyclovir, but with no known renal toxicity. Predictor Outpatient prescription for oral acyclovir, valacyclovir, or famciclovir. Outcomes The primary outcome was hospital admission with AKI in the 30 days after the initial prescription. Measurements We assessed the primary outcome with health care diagnostic codes. In a subpopulation, we assessed AKI using available laboratory serum creatinine measurements. Results 76,269 patients received acyclovir or valacyclovir and 84,646 received famciclovir. On average, patients were aged 76 [IQR, 71-81] years and prescription duration was 7 days. Acyclovir or valacyclovir use was not associated with a higher risk of hospital admission with AKI (209 [0.27%] events with acyclovir or valacyclovir vs 238 [0.28%] events with famciclovir [relative risk, 0.97; 95% CI, 0.81-1.17]). Results were consistent in adjusted analyses, in all subgroups, and in the subpopulation with laboratory measurements. Limitations Diagnostic codes had high specificity but low sensitivity and underestimated the incidence of AKI. Only a limited number of patients (n = 2,729) had serum creatinine values available. Conclusions In this population-based study of older adults, oral acyclovir use was not associated with a higher risk of AKI compared to famciclovir.

Importance Without third-party insurance, access to marketed drugs is limited to those who can afford to pay. We examined this phenomenon in the context of anticoagulation for patients with nonvalvular atrial fibrillation (NVAF). Objective To determine whether, among older Ontarians receiving anticoagulation for NVAF, patients of higher socioeconomic status (SES) were more likely to switch from warfarin to dabigatran prior to its addition to the provincial formulary. Design, Setting and Participants Population-based retrospective cohort study of Ontarians aged 66 years and older, between 2008 and 2012. Exposure Socioeconomic status, as approximated by median neighborhood income. Main Outcomes and Measure We identified two groups of older adults with nonvalvular atrial fibrillation: those who appeared to switch from warfarin to dabigatran after its market approval but prior to its inclusion on the provincial formulary (“switchers”), and those with ongoing warfarin use during the same interval (“non-switchers”). Results We studied 34,797 patients, including 3183 “switchers” and 31,614 “non-switchers”. We found that higher SES was associated with switching to dabigatran prior to its coverage on the provincial formulary (p

Background. There are no Canadian prevalence studies on pulmonary arterial hypertension (PAH) to date. We described the characteristics of treated PAH patients and the healthcare utilization and costs associated with PAH in a population of public drug plan beneficiaries in Ontario, Canada.Methods. A retrospective cross-sectional analysis was conducted between April 2010 and March 2011 to identify treated PAH patients using population-based health administrative databases. We investigated demographic and clinical characteristics of treated PAH patients and conducted a cohort study to determine treatment patterns, healthcare utilization, and associated costs, over a one-year follow-up period (March 2012).Results. We identified 326 treated PAH cases in Ontario’s publicly funded drug plan. Overall mean age was 59.4 years (±20.3 years) and over 77% of cases were women (n=251). Combination therapy was used to treat 22.9% (n=69) of cases, costing an average of $4,569 (SD $1,544) per month. Median monthly healthcare costs were $264 (IQR $96–$747) for those who survived and $2,021 (IQR $993–$6,399) for those who died over a one-year period, respectively (p<0.01).Conclusions. PAH care in Ontario is complex and has high healthcare costs. This data may help guide towards improved patient management.

6 Background: Emergency department (ED) visits and hospitalizations are undesirable and costly. We developed and validated the PROACCT (PRediction Of Acute Care use during Cancer Treatment) score to predict at least one acute care visit during the first 30 days (AC30) after initiating systemic therapy for cancer. Methods: Using administrative data, we identified patients in Ontario with the 18 most common solid tumors who started systemic treatment from July 1, 2014 to June 30, 2015. Southwestern and Northeastern Ontario formed the development and validation cohorts, respectively. We created a score to predict AC30 using multivariate logistic regression in the development cohort. Combinations of tumor sites and regimens were grouped into quintiles based on AC30. The score was assessed in the validation cohort. Results: AC30 occurred in 23% (4438/19359) of patients. Eleven factors predicted AC30 and formed the score: tumor site and regimen (2nd quintile: 2; 3rd-4th: 3; 5th: 4), recent ED visit (2), recent palliative radiation (1), rural residence (1) and Edmonton Symptom Assessment Scale anxiety (4+: 1), lack of appetite (4+: 1), pain (4+: 1), and wellbeing (4+: 1). Among the 204 tumor-regimen combinations, tumors with poor prognoses, such as pancreatic and lung, and platinum- and taxane-containing regimens, carried the highest risk for AC30. The score had moderate discrimination (c-statistic 0.65; P< 0.001) and strong calibration (Table) in the validation cohort. Conclusions: PROACCT identifies factors that predict AC30 in patients starting systemic treatment for solid tumors and could be incorporated into electronic health records to select patients for preventative interventions. [Table: see text]

BRAF V600E hyperactivates ERK and signals as an RAF inhibitor-sensitive monomer. While RAF inhibitors can produce impressive clinical responses in patients with mutant BRAF tumors, the mechanisms of resistance to these drugs are incompletely characterized. Here, we report a complete response followed by clinical progression in a patient with a BRAF V600E-mutant brain tumor treated with dabrafenib. Whole-exome sequencing revealed a secondary BRAF L514V mutation at progression that was not present in the pretreatment tumor. Expressing BRAF V600E L514V induces ERK signaling, promotes RAF dimer formation, and is sufficient to confer resistance to dabrafenib. A novel class of RAF dimer inhibitors and an ERK inhibitor are effective against BRAF L514V-mediated resistance. Collectively, our results validate a novel biochemical mechanism of RAF inhibitor resistance mediated by a secondary mutation, emphasizing that like driver mutations in cancer, the spectrum of mutations that drive resistance to targeted therapy are heterogeneous and perhaps emerge with a lineage-specific prevalence. Citation Format: Jiawan Wang, Zhan Yao, Philip Jonsson, Amy Allen, Alice Can Ran Qin, Sharmeen Uddin, Ira J. Dunkel, Mary Petriccione, Katia Manova, Sofia Haque, Marc Rosenblum, David J. Pisapia, Neal Rosen, Barry S. Taylor, Christine A. Pratilas. A secondary mutation in BRAF confers resistance to RAF inhibition in a BRAF V600E-mutant brain tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3184.

10014Background: AYA cancer survivors are at elevated risk for developing therapy-related adverse health outcomes and require life-long risk-adapted health care. We determined the location and prov...

BRAF V600E drives tumors by hyperactivating ERK signaling, is activated in a RAS-independent manner, and signals as a monomer. Selective inhibitors of RAF potently inhibit BRAF V600E and downstream ERK signaling, and have been associated with impressive clinical responses in patients whose tumors harbor V600E mutations in BRAF. Almost all patients, however, ultimately develop resistance. To date, acquired resistance mechanisms validated in patient samples have included splice forms of BRAF, mutations in NRAS, and BRAF amplification, all of which promote formation of RAF dimers, and mutations in MEK. Second-site point mutations in BRAF that promote dimer formation and are associated with acquired resistance have not previously been identified in RAF inhibitor-resistant tumors. Here, we report a complete response followed by clinical progression of a BRAF V600E-mutant pediatric brain tumor treated with the RAF inhibitor dabrafenib. We identified a second-site mutation in BRAF at the time of progression that was not present in the pretreatment tumor. Further study indicated the acquired mutation is in cis with V600E. We demonstrate that the acquired resistance mutation induces RAF dimer formation, and is sufficient to confer resistance to dabrafenib. Moreover, we showed that ERK signaling activated by the double mutation is sensitive to MEK inhibition or to the RAF plus and MEK inhibitor combination. We also find that two novel RAF dimer inhibitors may overcome resistance mediated by the novel mutation in BRAF. This is the first study, to our knowledge, that demonstrates the emergence of a confirmed second-site mutation in BRAF V600E and validates that this mutation is responsible for acquired resistance in an initially responding patient treated with dabrafenib. The mechanism of acquired resistance can be abrogated by the novel RAF dimer inhibitors. Our data confirm that a novel class of RAF dimer inhibitors are active against an acquired resistance mutation, suggesting an improved personalized treatment option for patients who harbor similar second-site mutations in BRAF. Citation Format: Jiawan Wang, Zhan Yao, Philip Jonsson, Amy Allen, Alice Can Ran Qin, David Pisapia, Neal Rosen, Barry S. Taylor, Christine A. Pratilas. A second-site mutation in BRAF confers resistance to RAF inhibition in a BRAF V600E-mutant brain tumor [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A129.

Purpose No effective systemic therapy exists for patients with metastatic low-grade serous (LGS) ovarian cancers. BRAF and KRAS mutations are common in serous borderline (SB) and LGS ovarian cancers, and MEK inhibition has been shown to induce tumor regression in a minority of patients; however, no correlation has been observed between mutation status and clinical response. With the goal of identifying biomarkers of sensitivity to MEK inhibitor treatment, we performed an outlier analysis of a patient who experienced a complete, durable, and ongoing (> 5 years) response to selumetinib, a non-ATP competitive MEK inhibitor. Patients and Methods Next-generation sequencing was used to analyze this patient's tumor as well as an additional 28 SB/LGS tumors. Functional characterization of an identified novel alteration of interest was performed. Results Analysis of the extraordinary responder's tumor identified a 15-nucleotide deletion in the negative regulatory helix of the MAP2K1 gene encoding for MEK1. Functional characterization demonstrated that this mutant induced extracellular signal-regulated kinase pathway activation, promoted anchorage-independent growth and tumor formation in mice, and retained sensitivity to selumetinib. Analysis of additional LGS/SB tumors identified mutations predicted to induce extracellular signal-regulated kinase pathway activation in 82% (23 of 28), including two patients with BRAF fusions, one of whom achieved an ongoing complete response to MEK inhibitor–based combination therapy. Conclusion Alterations affecting the mitogen-activated protein kinase pathway are present in the majority of patients with LGS ovarian cancer. Next-generation sequencing analysis revealed deletions and fusions that are not detected by older sequencing approaches. These findings, coupled with the observation that a subset of patients with recurrent LGS ovarian cancer experienced dramatic and durable responses to MEK inhibitor therapy, support additional clinical studies of MEK inhibitors in this disease.

Histiocytic neoplasms are clonal, hematopoietic disorders characterized by an accumulation of abnormal, monocyte-derived dendritic cells or macrophages in Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (non-LCH), respectively. The discovery of BRAFV600E mutations in approximately 50% of these patients provided the first molecular therapeutic target in histiocytosis. However, recurrent driving mutations in the majority of patients with BRAFV600E–wild-type non-LCH are unknown, and recurrent cooperating mutations in non-MAP kinase pathways are undefined for the histiocytic neoplasms. Through combined whole-exome and transcriptome sequencing, we identified recurrent kinase fusions involving BRAF, ALK, and NTRK1, as well as recurrent, activating MAP2K1 and ARAF mutations in patients with BRAFV600E–wild-type non-LCH. In addition to MAP kinase pathway lesions, recurrently altered genes involving diverse cellular pathways were identified. Treatment of patients with MAP2K1- and ARAF-mutated non-LCH using MEK and RAF inhibitors, respectively, resulted in clinical efficacy, demonstrating the importance of detecting and targeting diverse kinase alterations in these disorders. Significance: We provide the first description of kinase fusions in systemic histiocytic neoplasms and activating ARAF and MAP2K1 mutations in non-Langerhans histiocytic neoplasms. Refractory patients with MAP2K1- and ARAF-mutant histiocytoses had clinical responses to MEK inhibition and sorafenib, respectively, highlighting the importance of comprehensive genomic analysis of these disorders. Cancer Discov; 6(2); 154–65. ©2015 AACR. This article is highlighted in the In This Issue feature, p. 109

The aim of this study was to investigate the safety and efficacy of a heparin drug delivery system (HEP DDS) for prevention of posterior capsular opacification (PCO) in rabbits.Fifty New Zealand albino rabbits (50 eyes) undergoing phacoemulsification were equally divided into five groups receiving normal saline eye drops (group A), a carrier DDS implanted into the posterior chamber (group B), 5% heparin eye drops (group C), a HEP DDS implanted subconjunctivally (group D) and a HEP DDS implanted into the posterior chamber (group E). All the 50 eyes were examined by slit-lamp microscopy. The heparin levels in blood and aqueous humor were measured, and the wet posterior capsules were weighed.All eyes in groups A and B had PCO at 5-7 days, much earlier than in groups C, D and E. Two eyes in group C, three eyes in group D and six eyes in group E showed no signs of PCO throughout the 12-week study. The mean weight of wet posterior capsules from groups A-E was 157.919 mg, 160.091 mg, 81.114 mg, 71.827 mg and 19.984 mg respectively. The mean aqueous humor heparin level in groups C, D and E was 10.279 microg/ml, 13.246 microg/ml and 25.964 microg/ml respectively. Cell proliferation of the posterior capsules in group E was not active. The conjunctiva, cornea, iris, ciliary body and retina remained intact, and no significant toxic reactions were observed. No intraocular hemorrhage occurred during the follow-up.Implantation of a HEP DDS into the posterior chamber of experimental animals significantly maintained a higher heparin level in aqueous humor for a relatively long period of time. The findings indicate potential prevention of PCO with minimum toxic and side effects.

Activating BRAF mutants drive human tumors by dysregulating ERK signaling despite ERK-dependent feedback suppression of RAS. These RAF mutants become RAS independent, by either of two mechanisms, and they are thus unaffected by feedback inhibition of upstream signaling. Recently, it has become clear that mutation activation of MEK1 or MEK2 occur at appreciable frequency in human tumors, but the mechanism of activation of these mutants and whether they remain dependent on upstream activation of RAS or RAF signaling remains unknown. Here we characterized the mechanism of activation of 18 recurrent MEK1 mutants identified in human cancer. Based on these data, they fall into three classes. The kinase activity of first class remains dependent on RAF mediated phosphorylation of S218 and S222; the second class of MEK mutants has basal RAF-independent activity, but can be further stimulated by RAF and the third class no longer requires phosphorylation of S218 and S222 and signals in a RAF independent manner. These features determined their sensitivity to ERK-dependent feedback regulation and the ability to drive ERK signaling output in cells. The more RAF-independent activity the mutants acquired, the better they could activate downstream ERK pathway, leading to increased transforming activities in MEF cells in the absence of RAF. This is consistent with their genetic association with RAS, RAF and NF1 mutations in human tumors. The Class 3 RAF-independent MEK1 mutants tend to be mutually exclusive with those mutants, while coexistence with RAS/RAF/NF1 mutations is frequently observed in tumors with Class 1 or 2 MEK1 mutants. Moreover, functional class correlated with sensitivities of ERK signaling driven by these mutants to MEK inhibitors that function by different mechanisms. Unlike RAF dependent or regulated MEK1 mutants, the ERK signaling driven by RAF independent MEK1 mutants is insensitive to an allosteric MEK inhibitor that functions by preventing RAF mediated MEK phosphorylation. However, signaling driven by all classes of MEK1 mutants is sensitive to an ATP competitive MEK1 inhibitor which targets MEK1 kinase activity. Citation Format: Yijun Gao, Matthew T. Chang, Daniel McKay, Rona D. Yaeger, Merna Torres, Keven Muniz, Drosten Matthias, Omar I. Abdel-Wahab, Mariano Barbacid, Giordano Caponigro, Darrin Stuart, David Solit, Barry S. Taylor, Zhan Yao, Neal Rosen. Activation mechanisms of cancer associated MEK1 mutants [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 395. doi:10.1158/1538-7445.AM2017-395

Approximately two hundred mutant BRAF alleles have been identified in human tumors. Physiologic activation of RAF isoforms requires RAS-dependent induction of their dimerization. Activating BRAF mutants cause ERK dependent feedback inhibition of RAS.GTP and are RAS independent. As we have shown previously, they signal either as active monomers or RAS-independent constitutively active dimers. Here, we characterized a third class of BRAF mutants—those that have impaired kinase activity or are kinase dead. These class 3 BRAF mutants are sensitive to ERK-mediated feedback and they function in a RAS-dependent manner. In tumors, they bind more tightly to active RAS, thus enhancing their heterodimerization with CRAF. This is associated with the amplification of RAS-RAF-MEK-ERK signaling. Since these mutants are sensitive to ERK-dependent feedback inhibition of RAS, their enhancement of ERK signaling in tumors requires concurrent dysregulation of RAS activation. Thus, melanomas with Class 3 mutations usually harbor coexistent RAS mutation or NF1 mutants/deletion, whereas receptor tyrosine kinase signaling is activated in lung and colorectal cancers with these mutants. Our model suggests that these tumors will be sensitive to the inhibition of RAS activation. Currently, no direct inhibitors of RAS activation are available. However, in support of this idea, inhibitors of activated RTK signaling in carcinomas with Class 3 BRAF mutants and wild type RAS is sufficient to markedly inhibit ERK signaling and their growth in in vivo murine models and in patients. We have thus defined a third subset of BRAF mutants, which is RAS-dependent. Tumors harboring such mutants are sensitive to tyrosine kinase inhibitors in tumors expressing wild type RAS and NF1. Citation Format: Zhan Yao, Rona Yaeger, Vanessa S. Rodrik-Outmezguine, Anthony Tao, Neilawattie M. Torres, Matthew T. Chang, Matthias Drosten, Huiyong Zhao, Fabiola Cecchi, Todd Hembrough, Judith Michels, Hervé Baumert, Linde Miles, Naomi M. Campbell, Elisa de Stanchina, David B. Solit, Mariano Barbacid, Barry S. Taylor, Neal Rosen. Tumors with class 3 BRAF mutants are sensitive to the inhibition of activated RAS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4078. doi:10.1158/1538-7445.AM2017-4078

BACKGROUND: Dabigatran etexilate is a prodrug whose absorption is opposed by intestinal P-glycoprotein and which is converted by carboxylesterase to its active form, dabigatran. Unlike other statins, simvastatin and lovastatin are potent inhibitors of P-glycoprotein and carboxylesterase, and might either increase the risk of hemorrhage with dabigatran etexilate or decrease its effectiveness. METHODS: We conducted 2 population-based, nested case–control studies involving Ontario residents 66 years of age and older who started dabigatran etexilate between May 1, 2012, and Mar. 31, 2014. In the first study, cases were patients with ischemic stroke; in the second, cases were patients with major hemorrhage. Each case was matched with up to 4 controls by age and sex. All cases and controls received a single statin in the 60 days preceding the index date. We determined the association between each outcome and the use of simvastatin or lovastatin, relative to other statins. RESULTS: Among 45 991 patients taking dabigatran etexilate, we identified 397 cases with ischemic stroke and 1117 cases with major hemorrhage. After multivariable adjustment, use of simvastatin or lovastatin was not associated with an increased risk of stroke (adjusted odds ratio [OR] 1.33, 95% confidence interval [CI] 0.88 to 2.01). In contrast, use of simvastatin and lovastatin were associated with a higher risk of major hemorrhage (adjusted OR 1.46, 95% CI 1.17 to 1.82). INTERPRETATION: In patients receiving dabigatran etexilate, simvastatin and lovastatin were associated with a higher risk of major hemorrhage relative to other statins. Preferential use of the other statins should be considered in these patients.

Melanoma is a disease characterized by lesions that activate ERK. Although 70% of cutaneous melanomas harbor activating mutations in the BRAF and NRAS genes, the alterations that drive tumor progression in the remaining 30% are largely undefined. Vemurafenib, a selective inhibitor of RAF kinases, has clinical utility restricted to BRAF-mutant tumors. MEK inhibitors, which have shown clinical activity in NRAS-mutant melanoma, may be effective in other ERK pathway-dependent settings. Here, we investigated a panel of melanoma cell lines wild type for BRAF and NRAS to determine the genetic alteration driving their transformation and their dependence on ERK signaling in order to elucidate a candidate set for MEK inhibitor treatment. A cohort of the BRAF/RAS wild type cell lines with high levels of RAS-GTP had loss of NF1, a RAS GTPase activating protein. In these cell lines, the MEK inhibitor PD0325901 inhibited ERK phosphorylation, but also relieved feedback inhibition of RAS, resulting in induction of pMEK and a rapid rebound in ERK signaling. In contrast, the MEK inhibitor trametinib impaired the adaptive response of cells to ERK inhibition, leading to sustained suppression of ERK signaling and significant antitumor effects. Notably, alterations in NF1 frequently co-occurred with RAS and BRAF alterations in melanoma. In the setting of BRAF(V600E), NF1 loss abrogated negative feedback on RAS activation, resulting in elevated activation of RAS-GTP and resistance to RAF, but not MEK, inhibitors. We conclude that loss of NF1 is common in cutaneous melanoma and is associated with RAS activation, MEK-dependence, and resistance to RAF inhibition. Cancer Res; 74(8); 2340–50. ©2014 AACR.

Background: Telmisartan, unlike other angiotensin-receptor blockers, is a partial agonist of peroxisome proliferator–activated receptor-γ, a property that has been associated with improvements in surrogate markers of cardiovascular health in small trials involving patients with diabetes. However, whether this property translates into a reduced risk of cardiovascular events and death in these patients is unknown. We sought to explore the risk of myocardial infarction, stroke and heart failure in patients with diabetes who were taking telmisartan relative to the risk of these events occurring in patients taking other angiotensin-receptor blockers. Methods: We conducted a population-based, retrospective cohort study of Ontario residents with diabetes aged 66 years and older who started treatment with candesartan, irbesartan, losartan, telmisartan or valsartan between Apr. 1, 2001, and Mar. 31, 2011. Our primary outcome was a composite of admission to hospital for acute myocardial infarction, stroke or heart failure. We examined each outcome individually in secondary analyses, in addition to all-cause mortality. Results: We identified 54 186 patients with diabetes who started taking an angiotensin-receptor blocker during the study period. After multivariable adjustment, patients who took either telmisartan (adjusted hazard ratio [HR] 0.85, 95% confidence interval [CI] 0.74–0.97) or valsartan (adjusted HR 0.86, 95% CI 0.77–0.95) had a lower risk of the composite outcome compared with patients who took irbesartan. In contrast, no significant difference in risk was seen between other angiotensin-receptor blockers and irbesartan. In secondary analyses, we found a reduced risk of admission to hospital for heart failure with telmisartan compared with irbesartan (adjusted HR 0.79, 95% CI 0.66–0.96), but no significant differences in risk were seen between angiotensin-receptor blockers in our other secondary analyses. Interpretation: Compared with other angiotensin-receptor blockers, telmisartan and valsartan were both associated with a lower risk of admission to hospital for acute myocardial infarction, stroke or heart failure among older adults with diabetes and hypertension. Telmisartan and valsartan may therefore be the preferred angiotensin-receptor blockers for use in these patients.

Background Some evidence suggests that chlorthalidone may be superior to hydrochlorothiazide for the treatment of hypertension. Objective To compare the effectiveness and safety of chlorthalidone and hydrochlorothiazide in older adults. Design Propensity score-matched observational cohort study with up to 5 years of follow-up. Setting Ontario, Canada. Patients All individuals aged 66 years or older who were newly treated with chlorthalidone or hydrochlorothiazide and were not hospitalized for heart failure, stroke, or myocardial infarction in the prior year were eligible for inclusion. Each chlorthalidone recipient was matched to up to 2 hydrochlorothiazide recipients on the basis of age, sex, year of treatment initiation, and propensity score. Measurements The primary outcome was a composite of death or hospitalization for heart failure, stroke, or myocardial infarction. Safety outcomes included hospitalization with hypokalemia or hyponatremia. Results A total of 29 873 patients were studied. During follow-up, chlorthalidone recipients (n = 10 384) experienced the primary outcome at a rate of 3.2 events per 100 person-years of follow-up, and hydrochlorothiazide recipients experienced 3.4 events per 100 person-years of follow-up (adjusted hazard ratio, 0.93 [95% CI, 0.81 to 1.06]). Patients treated with chlorthalidone were more likely to be hospitalized with hypokalemia (adjusted hazard ratio, 3.06 [CI, 2.04 to 4.58]) or hyponatremia (adjusted hazard ratio, 1.68 [CI, 1.24 to 2.28]). In 9 post hoc analyses comparing patients initially prescribed 12.5, 25, or 50 mg of chlorthalidone per day with those prescribed 12.5, 25, or 50 mg of hydrochlorothiazide per day, the former were more likely to be hospitalized with hypokalemia for all 6 comparisons in which a statistically significant association was found. The results of other effectiveness and safety outcomes were also consistent with those of the main analysis. Limitation Unmeasured differences in baseline characteristics or physician treatment approaches or an insufficiently large sample may have limited the ability to detect small differences in the comparative effectiveness of the drugs. Conclusion As typically prescribed, chlorthalidone in older adults was not associated with fewer adverse cardiovascular events or deaths than hydrochlorothiazide. However, it was associated with a greater incidence of electrolyte abnormalities, particularly hypokalemia. Primary funding source Ontario Ministry of Health and Long-Term Care.

Background The novel oral anticoagulants, including dabigatran and rivaroxaban, differ in their degree of renal excretion. Methods We conducted a population-based nested case-control study in patients 66 years and older with chronic kidney disease (CKD) (excluding patients undergoing chronic dialysis) who received an oral anticoagulant between April 2006 and March 2013. We calculated odds ratios for hospitalization with a major hemorrhagic event and receipt of dabigatran, rivaroxaban, or warfarin in the preceding 60 days. We also performed a sensitivity analysis to investigate whether a relationship exists between major hemorrhage and advanced age (age Results We identified 237,409 patients with CKD, 4470 (1.9%) of whom experienced a major hemorrhage. We matched these patients to 14,460 controls. The use of dabigatran or rivaroxaban was not associated with a statistically significant elevated risk of hemorrhage compared with warfarin (adjusted odds ratio [aOR], 1.15; 95% confidence interval [CI], 0.91-1.45 for dabigatran; aOR, 1.22; 95% CI, 0.83-1.79 for rivaroxaban). Our sensitivity analysis found that older age was associated with an increased risk of hemorrhage for patients receiving dabigatran (aOR, 1.41; 95% CI, 1.06-1.88); results were similar but did not reach statistical significance for rivaroxaban (aOR, 1.57; 95% CI, 0.91-2.69). Conclusions Among elderly patients with CKD, exposure to dabigatran or rivaroxaban was not associated with a statistically significant increased risk of major hemorrhagic events compared with exposure to warfarin.

Background: RAF and EGFR inhibitor combinations have shown promising clinical activity in patients with BRAF V600E colorectal cancer, but resistance invariably develops. Methods: To define mechanisms of resistance to RAF/EGFR inhibition, we analyzed pre-treatment and disease progression samples from patients with BRAF mutant colorectal cancer using our custom next-generation sequencing platform, MSK-IMPACT (Integrated Mutation Profiling of Actionable Cancer Targets). Cell line and patient derived xenograft models were generated to investigate the effects of the genetic alterations identified at disease progression. Results: We identified alterations predicted to result in RAF dimerization and re-activation of ERK signaling in seven of eight post-progression tumors. These alterations included an intragenic deletion in BRAF encompassing the RAS binding domain, KRAS and NRAS mutations, and KRAS, NRAS, and BRAF amplifications. Notably, these alterations were rapidly enriched in the presence of drug treatment but selected against in the absence of drug exposure. A novel RAF inhibitor, that equipotently inhibits RAF mutant monomers and dimers, effectively suppressed ERK signaling in the RAF/EGFR resistant colorectal tumors at drug doses that did not inhibit ERK signaling in RAS/RAF wild-type cells. Treatment with this novel RAF inhibitor was able to overcome resistance in cell line and patient derived xenograft models. Conclusions: Our data suggest that alterations that promote RAF dimers, which are resistant to first generation RAF inhibitors, are a unifying mechanism of RAF/EGFR inhibitor resistance in patients with BRAF mutant colorectal cancer. These results support the testing of RAF dimer inhibitors in combination with EGFR inhibitors in patients with BRAF V600E colorectal cancer. Citation Format: Rona Yaeger, Zhan Yao, David M. Hyman, Jaclyn F. Hechtman, Efsevia Vakiani, Andrea Cercek, Jose Baselga, Elisa DeStanchina, Leonard Saltz, Michael F. Berger, David B. Solit, Neal Rosen. RAF kinase dimerization mediates clinical acquired resistance to RAF/EGFR inhibition in BRAF V600E colorectal cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C174.

Background Embryo transfer is a crucial step in the IVF process. Most randomized prospective studies comparing transfer catheters have demonstrated significantly higher pregnancy rates with soft versus firm catheters, but none have taken the operator effect into account. Our aim was to perform a prospective randomized clinical trial comparing two catheters and to study interactions between catheters and operators. Methods A prospective randomized trial comparing the Cook K-SOFT-5100 and Frydman classical catheters 4.5 was performed. Three experienced operators participated in the trial, using a fixed distance transfer protocol. Primary end-point was clinical pregnancy rate, secondary end-points were rates of difficult transfer and of catheter failure. Patients were randomized by a computer program prior to embryo transfer. Results A total of 1446 embryo transfers were performed in 1155 women undergoing IVF or ICSI treatment. A total of 723 cycles were randomized to the Cook catheter and 723 cycles to the Frydman catheter. Following intention-to-treat analysis, the adjusted odds ratio of clinical pregnancy between for the Cook versus the Frydman catheter was 1.11 [95% confidence interval (95% CI) 0.89-1.38]. Odds ratios of clinical pregnancy between the Cook and Frydman catheters for the three operators were respectively 1.19 (95% CI 0.84-1.69), 2.35 (95% CI 1.40-3.95) and 0.69 (95% CI 0.48-0.99). Conclusions Variation in pregnancy rates between embryo transfer catheters depends on variation between operators. Results from randomized clinical trials comparing embryo transfer catheters should not be generalized, because inconsistent conclusions may be unavoidable on the account of different proportions of cycles with transfers by each type of operator. The study was registered at clinicaltrials.gov. NCT00766714.

BACKGROUND: We postulated that impaired endometrial differentiation in women with pelvic endometriosis predisposes for pre-eclampsia. METHODS: A retrospective case-control study set at the University of Ghent IVF centre. The incidence of pre-eclampsia and pregnancy-induced hypertension (PIH) following the clinical and/or laparoscopic diagnosis of endometriosis-associated infertility (case group; n = 245 pregnancies) was compared with the incidence of these obstetric complications in pregnancies following treatment for male-factor infertility (control group; n = 274 pregnancies). Pregnancy data were obtained by searching electronic databases and postal questionnaires. The case and control groups were matched for age, parity and multiple pregnancies. RESULTS: The incidence of pre-eclampsia was significantly lower in the case group (0.8%) when compared with control group (5.8%) (P = 0.002; odds ratio (OR) = 7.5, 95% confidence interval (CI): 1.7-33.3). Analysis of obstetric outcome in the subgroup of patients with laparoscopic data confirmed the lower risk of pre-eclampsia in the case (1.2 %) versus control (7.4 %) groups (P = 0.032; OR = 6.6, 95% CI: 1.2-37). PIH occurred in 3.5% and 8.7% of case and control pregnancies, respectively (P = 0.018; OR = 2.6, 95% CI: 1.2-6.0). The odds of developing pre-eclampsia were 5.67 times higher in the control group than in pregnancies following endometriosis-associated infertility. In multiple pregnancies, the odds of developing pre-eclampsia increased 1.93 times per additional child, with or without endometriosis. CONCLUSIONS: We found no evidence that endometriosis predisposes for pre-eclampsia. Instead, the risk of hypertensive disorder in pregnancy is significantly reduced in women with endometriosis-associated infertility.

Background Among patients taking warfarin, lower socioeconomic status is associated with poorer control of anticoagulation. However, the extent to which socioeconomic status influences the risk of hemorrhage is unknown. We examined the extent to which socioeconomic status influences the risk of hemorrhage in older individuals newly commencing warfarin therapy for atrial fibrillation. Methods We conducted a population-based cohort study of individuals 66 years or older with atrial fibrillation who commenced warfarin therapy between April 1, 1997, and November 30th 2011, in Ontario, Canada. We used neighborhood-level income quintiles as a measure of socioeconomic status. The primary outcome was an emergency department visit or hospitalization for hemorrhage, and the secondary outcome was fatal hemorrhage. Results We studied 166,742 older patients with atrial fibrillation who commenced warfarin therapy. Of these, 16,371 (9.8%) were hospitalized for hemorrhage during a median follow-up of 369 (interquartile range 102-865) days. After multivariable adjustment using Cox proportional hazards regression, we found that those in the lowest-income quintile faced an increased risk of hospitalization for hemorrhage relative to those in the highest quintile (adjusted hazard ratio 1.18, 95% CI 1.12-1.23). Similarly, the risk of fatal hemorrhage (n = 1,802) was increased in the lowest-income relative to the highest-income quintile (adjusted hazard ratio 1.28, 95% CI 1.11-1.48). Conclusions Among older individuals receiving warfarin therapy for atrial fibrillation, lower socioeconomic status is a risk factor for hemorrhage and hemorrhage-related mortality. This factor should be carefully considered when initiating and monitoring warfarin therapy.

PURPOSE: To investigate the relationship between muscular asthenopia and eccentric ablation after photorefractive keratectomy (PRK). METHODS: Sixteen eyes of eight myopic patients whose muscular asthenopia was corrected by subjectively accepted spectacle prism after PRK, with visual acuity better than 0.8, were followed for 6 to 14 months. On the basis of preoperative and postoperative data and corneal topography, we calculated the total corrected corneal power using the Holladay formula and then measured the ablation eccentricity (h, millimeters) and its direction. According to the formula δ ≅ Dh, the prism effective value (δ) caused by the eccentric ablation was computed and compared with the objectively accepted spectacle prism. RESULTS: The subjectively accepted spectacle prisms were similar to calculated values from the formula. Mean difference was 0.10 ± 0.25^sup Δ^. The direction of the subjectively accepted prism was in the direction of the ablation deviation. CONCLUSIONS: Eccentric ablation is an important cause of muscular visual asthenopia after PRK. The asthenopia may be corrected by spectacle prism. The spectacle prism value may be estimated by the formula δ ≅ Dh. [J Refract Surg 2001;17:380-382]

Though two-thirds of cutaneous melanomas harbor activating mutations in the BRAF and NRAS genes, the alterations that drive tumor progression in the roughly 30% of melanoma tumors wild-type for BRAF and NRAS remain largely uncharacterized. The selective RAF inhibitors vemurafenib and dabrafenib inhibit MAPK pathway activity only in BRAF mutant cells, thus their clinical utility is restricted to patients with BRAF mutant tumors. MEK inhibitors, which have broader antitumor activity and have shown promising activity in NRAS mutant melanoma, may be effective in a broader range of MAPK pathway-dependent tumors. We performed a functional and genomic analysis of melanoma cell lines wild-type for BRAF and NRAS to determine whether occult mutations in RAS signaling were present. Elevated RAS-GTP was common in BRAF/NRAS wild-type melanoma cell lines, a subset of which exhibited total loss of NF1 protein expression. The proliferation of NF1-null melanoma cells was dependent upon MEK, though the cellular potency of several allosteric MEK inhibitors that are currently in clinical testing (PD0325901, AZD6244, MEK162 and trametinib) varied widely in NF1-null melanoma cells. The greatest antitumor activity was noted with trametinib, a MEK inhibitor that also blocks RAF mediated phosphorylation of MEK. Notably, alterations in NF1 also co-occurred with RAS and BRAF mutations in both cell lines and human melanomas. In the setting of BRAF co-mutation, loss of NF1 abrogated upstream negative feedback on RAS activation resulting in constitutive expression of RAS-GTP and resistance to RAF but not MEK inhibition. In summary, NF1 loss is a common event in cutaneous melanoma that is associated with RAS activation, MEK dependence and RAF inhibitor resistance. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C138. Citation Format: Moriah H. Nissan, Christine Pratilas, Alexis Jones, Helen Won, Li Kong, Zhan Yao, Taha Merghoub, Antoni Ribas, Paul Chapman, Rona Yaeger, Barry Taylor, Nikolaus Shultz, Michael F. Berger, Neal Rosen, David B. Solit. Loss of NF1 in melanoma cell lines is associated with active Ras and dependence on MEK even in the absence of BRAF or NRAS mutation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C138.