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The increasingly widespread use of immunohistochemistry and next-generation sequencing (NGS) in the detection of microsatellite instability (MSI) and DNA mismatch repair (MMR) status has led to the observation of various unusual tumour types that exhibit MMR protein deficiency in Lynch syndrome (LS). Here, we report a case of two synchronous colorectal cancer (CRC) tumours simultaneously occurring in a 42-year-old woman with a deleterious germline mutation in MSH6, abundant expression of PD-L1 and high tumour mutation burden (TMB). The two CRC tumours (tumours A and B) harboured highly heterogeneous features. One showed loss of MSH6 protein and a microsatellite stable (MSS)/MSI-low (MSI-L) status, while the other presented no loss of MMR protein and MSI-H status. Furthermore, the 9 common mutated genes between the two CRC tumours had no shared mutation sites. Only 4 KEGG pathways were identified as enriched for five of the common mutated genes, while 8 cancer-related pathways were identified as enriched for 9 and 13 unique mutated genes in tumours A and B, respectively. Therefore, we chose immune checkpoint inhibitors (ICIs) as the potential therapy. This case exemplifies the complexity of tumorigenesis and potential ICI treatment in LS patients.

A 65-year-old, gravida 3, para 2 Japanese woman was referred to our hospital for symptomatic thickening of the endometrial lining. Endocervical and endometrial cytology revealed an adenocarcinoma. The endometrial biopsy specimen was mixed, with a glandular part diagnosed as endometrioid carcinoma and a solid part diagnosed as high-grade mixed large and small cell neuroendocrine carcinoma (L/SCNEC). She underwent extra-fascial hysterectomy with bilateral salpingo-oophorectomy, complete pelvic and para-aortic lymphadenectomy, and omentectomy (FIGO IIIB, pT3b pN0 M0). She currently has no deleterious germline mutation, but high tumor mutation burden and high microsatellite instability (MSI) were identified. She underwent six cycles of platinum-based frontline chemotherapy and achieved complete remission. Immune checkpoint blockade therapy is a promising second-line therapy for MSI-high solid tumors. However, the MSI or mismatch repair (MMR) status of endometrial L/SCNEC remains unclear in the literature. Universal screening for MSI/MMR status is needed, particularly for a rare and aggressive disease.

BACKGROUND: Germline mutations in genes mediating DNA repair are common in men with recurrent and advanced prostate cancer, and their presence may alter prognosis and management. We aimed to define pathological and clinical characteristics associated with germline DNA-repair gene mutations, to facilitate selection of patients for germline testing. METHODS: We retrospectively evaluated 150 unselected patients with recurrent or metastatic prostate cancer who were offered germline genetic testing by a single oncologist using a clinical-grade assay (Color Genomics). This platform utilizes next-generation sequencing from saliva to interrogate 30 cancer-susceptibility genes. Presence or absence of a deleterious germline mutation was correlated with histological and clinical characteristics, and with family history of cancer. All patients with DNA-sequence alterations (pathogenic or variants) were offered genetic counseling. RESULTS: Between July 2016 and July 2017, 150 consecutive patients underwent germline testing; pathogenic mutations were identified in 21 men (14%). Among those with germline mutations, 9 (43%) were in BRCA2, 3 (14%) were in ATM, 3 (14%) were in CHEK2, and 2 (9%) were in BRCA1. While there were no associations between germline mutations and age, tumor stage, Gleason sum or family history; mutation-positive patients had lower median PSA levels at diagnosis (5.5 vs 8.6ng/mL, P = 0.01) and unique pathologic features. Namely, men with germline mutations were more likely to harbor intraductal/ductal histology (48% vs 12%, P

There has been little improvement in the prognosis for adolescent and young adult (AYA) tumor patients. Hence, there is an urgent need to understand the etiology of tumor development and identify actionable gene aberrations to improve prevention and therapy. Here, 76 sporadic tumors (48 breast, 22 ovarian, and six uterine) from 76 AYA females (age range, 25-39 years) were subjected to whole exome and RNA sequencing to determine their mutational signatures and actionable gene profiles. Two individuals with breast cancer (4.2% of cases) and one with ovarian cancer (5.3% of cases) carried germline BRCA2 mutations. The two cases with breast tumors also each carried an additional deleterious germline mutation: one in TP53 and the other in CHEK2. Mutational signature analysis of the 76 tumors indicated that spontaneous deamination of 5-methylcytosine and activity of the APOBEC cytidine deaminase protein family are major causes of mutagenesis. In addition, 18 breast or ovarian tumors (18/70, 26%), including the three cases with germline BRCA2 mutations, exhibited a predominant "BRCAness" mutational signature, an indicator of functional BRCA1/BRCA2 deficiency. Actionable aberrations and high tumor mutation burdens were detected in 24 breast (50%), 17 ovarian (77%), and five uterine (83%) tumor cases. Thus, mutational processes and aberrant genes in AYA tumors are largely shared with those identified in non-AYA tumors. The efficacy of molecular targeting and immune checkpoint inhibitory therapies should be explored for both AYA and non-AYA patients.

Purpose Deleterious germline mutations contribute to pancreatic cancer susceptibility and are well documented in families in which multiple members have had pancreatic cancer. Methods To define the prevalence of these germline mutations in patients with apparently sporadic pancreatic cancer, we sequenced 32 genes, including known pancreatic cancer susceptibility genes, in DNA prepared from normal tissue obtained from 854 patients with pancreatic ductal adenocarcinoma, 288 patients with other pancreatic and periampullary neoplasms, and 51 patients with non-neoplastic diseases who underwent pancreatic resection at Johns Hopkins Hospital between 2000 and 2015. Results Thirty-three (3.9%; 95% CI, 3.0% to 5.8%) of 854 patients with pancreatic cancer had a deleterious germline mutation, 31 (3.5%) of which affected known familial pancreatic cancer susceptibility genes: BRCA2 (12 patients), ATM (10 patients), BRCA1 (3 patients), PALB2 (2 patients), MLH1 (2 patients), CDKN2A (1 patient), and TP53 (1 patient). Patients with these germline mutations were younger than those without (mean ± SD, 60.8 ± 10.6 v 65.1 ± 10.5 years; P = .03). Deleterious germline mutations were also found in BUB1B (1) and BUB3 (1). Only three of these 33 patients had reported a family history of pancreatic cancer, and most did not have a cancer family history to suggest an inherited cancer syndrome. Five (1.7%) of 288 patients with other periampullary neoplasms also had a deleterious germline mutation. Conclusion Germline mutations in pancreatic cancer susceptibility genes are commonly identified in patients with pancreatic cancer without a significant family history of cancer. These deleterious pancreatic cancer susceptibility gene mutations, some of which are therapeutically targetable, will be missed if current family history guidelines are the main criteria used to determine the appropriateness of gene testing.

SUMMARY Neurodevelopmental disorders are often caused by chromosomal microdeletions comprising numerous contiguous genes. A subset of neurofibromatosis type 1 (NF1) patients with severe developmental delays and intellectual disability harbors such a microdeletion event on chromosome 17q11.2, involving the NF1 gene and flanking regions (NF1 total gene deletion [NF1-TGD]). Using patient-derived human induced pluripotent stem cell (hiPSC)-forebrain cerebral organoids (hCOs), we identify both neural stem cell (NSC) proliferation and neuronal maturation abnormalities in NF1-TGD hCOs. While increased NSC proliferation results from decreased NF1/RAS regulation, the neuronal differentiation, survival, and maturation defects are caused by reduced cytokine receptor-like factor 3 (CRLF3) expression and impaired RhoA signaling. Furthermore, we demonstrate a higher autistic trait burden in NF1 patients harboring a deleterious germline mutation in the CRLF3 gene (c.1166T>C, p.Leu389Pro). Collectively, these findings identify a causative gene within the NF1-TGD locus responsible for hCO neuronal abnormalities and autism in children with NF1., Graphical Abstract, In brief To critically evaluate the impact of NF1 locus genomic microdeletion (17q11.2) on the development of human brain cells, Wegscheid et al. generated patient-derived hiPSC forebrain cerebral organoids (hCOs). Although increased hCO neural stem cell proliferation is RAS-dependent, the neuronal survival, differentiation, and maturation defects resulted from reduced CRLF3-dependent RhoA activation.

Endometrial cancer in the lower uterine segment (LUS) is associated with Lynch syndrome with MLH1 or MSH2 germline mutation. Here, we report a case of carcinoma of the LUS diagnosed with Lynch syndrome based on MSH6 germline mutation in a 46-year-old woman with abnormal vaginal bleeding. She had had rectal cancer at age 39 with a family history of colon cancer (father, 75 years), pancreatic cancer (paternal grandmother, 74 years), and colon cancer (maternal grandmother, 85 years). Magnetic resonance imaging showed a tumor in the LUS. Endometrial biopsy revealed endometrioid adenocarcinoma G1. As her cancer history met the revised Bethesda criteria, we examined microsatellite instability and the result was negative, but loss of the MSH6 expression was detected by immunohistochemistry. Genetic testing revealed deleterious germline mutation of MSH6, which was compatible with Lynch syndrome. To our knowledge, this is the first case of endometrial carcinoma of the LUS with MSH6 germline mutation.

We read with interest the work by Yan et al published in Gut .1 The serrated (hyperplastic) polyposis syndrome (SPS) is a heterogeneous disease defined by the presence of multiple serrated polyps throughout the colon,2 causing an increased risk (16%) of colorectal cancer (CRC).3 By performing whole-exome sequencing in 20 SPS families, Gala et al identified a germline mutation, c.338C>A (p.R113*), in the RING-type E3 ubiquitin ligase RNF43, an inhibitor of the Wnt pathway, in two independent families.4 The c.394C>T (p.R132*) mutation was subsequently identified in two SPS-affected members of one family, supporting a causal role in SPS.5 In the study by Yan et al whole-exome sequence analysis of four SPS families identified a deleterious germline mutation, c.953–1G>A (p.E318fs), in six members of one family, five fulfilling the WHO criteria for SPS.1 Buchanan et al assessed the mutation status of RNF43 in 74 selected SPS families, identifying two rare missense variants, c.443C>G (p.A148G) and c.640C>G (p.L214V), predicted deleterious by in silico algorithms, in two families. No carriers of p.R113* or p.R132* were detected in 221 additional patients with SPS.6 Mutation screening of RNF43 was carried out by Sanger sequencing in …

BACKGROUND: About 5% of pancreatic ductal adenocarcinomas are inherited due to a deleterious germline mutation detected in 20% or fewer families. Pancreatic screening in high-risk individuals is proposed to allow early surgical treatment of (pre)malignant lesions. The outcomes of pancreatic surgery in high-risk individuals have never been correctly explored. OBJECTIVES: To evaluate surgical appropriateness and search for associated factors in high-risk individuals. METHODS: A patient-level meta-analysis was performed including studies published since 1999. Individual classification distinguished the highest risk imaging abnormality into low-risk or high-risk abnormality, and the highest pathological degree of malignancy of lesions into no/low malignant potential or potentially/frankly malignant. Surgical appropriateness was considered when potentially/frankly malignant lesions were resected. RESULTS: Thirteen out of 24 studies were selected, which reported 90 high-risk individuals operated on. Low-risk/high-risk abnormalities were preoperatively detected in 46.7%/53.3% of operated high-risk individuals, respectively. Surgical appropriateness was consistent in 38 (42.2%) high-risk individuals, including 20 pancreatic ductal adenocarcinomas (22.2%). Identification of high-risk abnormalities was strongly associated with surgical appropriateness at multivariate analysis (P = 0.001). We proposed a score and nomogram predictive of surgical appropriateness, including high-risk abnormalities, age and existence of deleterious germline mutation. CONCLUSION: Overall, 42.2% of high-risk individuals underwent appropriate surgery. The proposed score might help selecting the best candidates among high-risk individuals for pancreatic resection.

Lynch syndrome (LS) is a hereditary cancer predisposition condition caused by inactivating germline mutations in one of the DNA mismatch repair (MMR) genes. Identifying a deleterious germline mutation by DNA sequencing is important for confirming an LS diagnosis. Frameshift and nonsense mutations significantly alter the protein product and likely impair MMR function. However, the implication of a missense mutation is often difficult to interpret. Referred to as variants of uncertain significance (VUS), their discovery hampers the definitive LS diagnosis. To determine the pathogenic significance of a VUS it is helpful to know its impact on protein function. Functional studies in the test tube and in cellular models have been performed for some VUS, however, these studies have been limited by the artificial nature of the assays. We report here an improved functional assay in which we engineered site-specific MSH2 VUS using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 gene editing in human embryonic stem cells. This approach introduces the variant into the endogenous MSH2 loci, while simultaneously eliminating the wild-type gene. We then characterized the impact of the variants on cellular MMR functions including DNA damage response signaling upon challenge with a DNA alkylating agent and the repair of DNA microsatellites. We classified the MMR functional capability of 8 of 10 VUS under study providing valuable information for determining their likelihood of being bona fide LS mutations. This improved human cell-based assay system for functionally testing MMR gene VUS will facilitate the identification of high risk LS patients.Significance StatementUnderstanding how cancer-associated missense variants in MMR genes affect function helps determine whether they truly contribute to disease. Laboratory assays previously utilized are limited by their artificial nature. To improve this, we introduced variants directly into the endogenous MMR loci in hESCs using CRISPR-Cas9 gene editing. This approach allows us to assess each variant while being expressed by its normal regulatory elements in a cellular environment. Our results will help guide the management of patients world-wide who carry these variants. At the same time, this study provides a technical road map for assessing the functional effects of all LS-associated variants, as well as variants linked to other genetic diseases where a cell-based functional assay is available.

Knowledge about the germline mutational spectrum among Brazilian with hereditary breast and ovarian cancer (HBOC) is limited. Only five studies have performed comprehensive BRCA sequencing, corresponding to 1041 individuals among a Brazilian population of over 207 million people. Herein we aimed to determine the clinical and molecular characteristics of Brazilian patients who underwent oncogenetic counseling and genetic testing of a panel of high-risk and moderate-risk genes from 2009 to 2017. Massively parallel sequencing was applied in 157 individuals (132 breast cancer-affected and 25 breast cancer-unaffected individuals) selected according NCCN criteria for hereditary breast cancer. Analysis of mutation segregation in family members was performed by capillary bidirectional sequencing, clinical response after treament and survival analysis was estimated by Kaplan–Meier. Nineteen germline variants were identified,15 pathogenic and 4 VUS (Variants of Uncertain Significance) in 27 individuals (27/157; 17% P < 0.0001) distributed among 7 genes. Sixty-eight percent of patients (13/19) harbor mutation in BRCA genes and 32% (6/19) in moderate risk genes. This is the first study reporting ATR deleterious germline mutation in association with hereditary breast cancer. Cancer-affected patients with moderate- risk mutation present a more aggressive phenotype, with bilateral cancer (25% vs. 13%, P = 0.0305), high-grade tumors (79.2% vs. 46.3%, P = 0.0001) and triple-negative (50% vs. 22.4%, P < 0.0001). However, no difference in the 5 years overall survival was observed between BRCA and moderate risk groups. This work highlights the benefits of large-scale sequencing for oncogenetic counseling and extends our understanding about the genetics of hereditary breast cancer in the multi-ethnic Brazilian population.

Pancreatic cancer is projected to become the second leading cause of cancer death in the United States by 2030. Deleterious germline mutations can contribute to pancreatic cancer susceptibility. Herein we report a case of a patient with metastatic pancreatic adenocarcinoma to the lung and liver who was found to have a deleterious germline mutation in RAD51C who had a remarkable response to chemotherapy with FOLFIRINOX, a platinum-containing regimen.

Cancer initiation and progression is the result of an accumulation of mutations in key tumor suppressor genes, mismatch repair genes, or oncogenes, which impact cancer cell growth, death, and differentiation. Mutations occurring in cancer tissue are termed somatic; whereas, heritable mutations that may be passed onto subsequent generations occur in germline DNA. It is these germline mutations that can lead to cancer family syndromes whereby family members carrying a deleterious germline mutation have an increased susceptibility to certain cancer phenotypes. Common features of hereditary cancer syndromes include early age-of-onset, multiple affected generations, rare tumor types, and/or multiple primary malignancies. Approximately, 5%–10% of all common cancers, including prostate cancer, have a hereditary component and are attributable to highly penetrant germline mutations.1 Across all cancer types, known cancer susceptibility syndromes number >100; however, it is important to note that mutations in high-penetrance genes explain only a fraction of heritable cancers.2 Well-known examples of hereditary cancer syndromes include Lynch (HNPCC), Cowden (PHTS), Li-Fraumeni, and Hereditary Breast and Ovarian Cancer (HBOC) syndromes, which are attributable to mutations in mismatch repair genes, PTEN, p53, and BRCA1/2, respectively.3

Germline mutations in BRCA1 and BRCA2 account for approximately 50% of inherited breast and ovarian cancers. Three founder mutations in BRCA1/2 have been reported in Colombia, but the pattern of mutations in other cancer susceptibility genes is unknown. This study describes the frequency and type of germline mutations in hereditary breast and/or ovarian cancer genes in a referral cancer center in Colombia. Eighty-five women referred to the oncogenetics unit of the Instituto de Cancerologia Las Americas in Medellin (Colombia), meeting testing criteria for hereditary breast and ovarian cancer syndrome (NCCN 2015), who had germline testing with a commercial 25-gene hereditary cancer panel, were included in the analysis. Nineteen patients (22.4%) carried a deleterious germline mutation in a cancer susceptibility gene: BRCA1 (7), BRCA2 (8), PALB2 (1), ATM (1), MSH2 (1) and PMS2 (1). The frequency of mutations in BRCA1/2 was 17.6%. One BRCA2 mutation (c.9246dupG) was recurrent in five non-related individuals and is not previously reported in the country. Seventeen mutation-carriers had a diagnosis of breast cancer (median age of diagnosis of 36 years) and two of ovarian cancer. All BRCA1 mutation-carriers with breast cancer had triple negative tumors (median age of diagnosis of 31 years). Variants of unknown significance were reported in 35% of test results. This is the first report of a multi-gene study for hereditary breast and/or ovarian cancer in a Latin American country. We found a high frequency and a wide spectrum of germline mutations in cancer susceptibility genes in Colombian patients, some of which were not previously reported in the country. We observed a very low frequency of known Colombian founder BRCA1/2 mutations (1.2%) and we found mutations in other genes such as PALB2, ATM, MSH2 and PMS2. Our results highlight the importance of performing multi-gene panel testing, including comprehensive BRCA1/2 analysis (full gene sequencing and large rearrangement analysis), in high-risk breast and/or ovarian cancer patients in Colombia.

Uveal melanoma arises from melanocytes of the uveal tract (iris, ciliary body and choroid) and represents the most common intraocular malignancy in adults. Some rare clinical situations (young age at diagnosis, bilateral or multifocal forms, association with cutaneous malignant melanoma and/or familial aggregations of melanomas) are suggestive of genetic susceptibility. The aim of this study was to evaluate the contribution of CDKN2A/P16INK4A, P14ARF and CDK4 gene germline mutations in a series of patients with uveal melanoma recruited in a single institution with a clinical presentation indicative of genetic predisposition. Molecular analyses were proposed to 36 patients and were performed in 25 cases. The contribution of BRCA1/2 gene germline mutations in patients with uveal melanoma and a personal and/or family history of breast/ovarian cancers was also evaluated. Molecular analysis of BRCA1/2 genes was proposed to 35 patients and was performed in 25 patients. No deleterious germline mutation was identified in either group of patients. These results indicate that the CDKN2A/P16INK4A, P14ARF, CDK4 genes are not responsible for the vast majority of genetic susceptibility to uveal melanoma. They also suggest that one case of uveal melanoma in a family with a history of breast cancer is not sufficient to justify BRCA1/2 genetic testing when the classical criteria for molecular analysis are not present. International studies are ongoing in melanoma-prone families in an attempt to identify uveal melanoma susceptibility loci and genes.

DICER1 syndrome is an inherited disorder associated with at least a dozen rare, mainly pediatric-onset tumors. Its characterization remains incomplete. Some studies suggested that neuroblastoma (NB) may be involved in this syndrome. Here, we describe the case of a 14-year-old female presenting with a multinodular goiter (MNG) and a collision tumor composed of NB and cystic nephroma (CN). She is a carrier of a deleterious germline mutation in exon 23 of DICER1 and harbored different somatic mutations in the CN and MNG. However, no second hit was found in the NB, questioning its status as a DICER1-related tumor.

Mutations of DNA mismatch repair genes are characterised by microsatellite instability and are implicated in carcinogenesis. This mutation susceptible phenotype has been extensively studied in patients with hereditary non-polyposis colon carcinoma, but little is known of the contribution of such mutations in other tumour types, particularly non-small-cell lung carcinoma. This report describes the occurrence of two synchronous lung tumours, one mimicking a metastatic colon carcinoma, in a male patient with a history of metachronous colonic carcinoma. Immunohistochemistry supported a pulmonary origin for both lesions. Mismatch repair protein immunohistochemistry showed loss of MSH2 and MSH6 expression in both colonic tumours and in one lung tumour showing enteric differentiation. Subsequent mutational analysis demonstrated a deleterious germline mutation of the MSH2 mismatch repair gene. The significance of these findings and the practical diagnostic difficulties encountered in this case are discussed.

Purpose Age younger than 50 years at the time of colon cancer diagnosis is often used as a screening criterion for Lynch syndrome (hereditary nonpolyposis colorectal cancer syndrome). The purpose of this study was to determine the prevalence of MLH1, MSH2, and MSH6 mutations in an unselected cohort of women diagnosed with endometrial cancer at age younger than 50 years. Methods A prospective, multicenter study was performed at three institutions. After written consent was obtained, germline mutation testing by full sequencing and large deletion analysis of the MLH1, MSH2, and MSH6 genes was performed. Tumor studies included immunohistochemistry of MLH1, MSH2, and MSH6; microsatellite instability analysis; and hypermethylation of the MLH1 promoter. Results Of the 100 women, nine (9%; 95% CI, 4.2 to 16.4) carried a deleterious germline mutation: seven women with mutations in MSH2, one woman with a mutation in MLH1, and one woman with a mutation in MSH6. Two additional women had molecular studies consistent with the diagnosis of Lynch syndrome. The mean body mass index (BMI) for the entire cohort was 34.4, which is significantly higher than 29.2, the mean BMI for the mutation carriers. Predictors of finding a germline mutation included having a first-degree relative with a Lynch syndrome–associated cancer, endometrial tumor with loss of MSH2 expression, tumors with high microsatellite instability, and lower BMI. Conclusion In this prospective study of endometrial cancer patients younger than age 50 years, 9% were found to carry germline Lynch syndrome–associated mutations. In addition to young age of onset, family history, BMI, and molecular tumor studies can improve the likelihood of identifying a Lynch syndrome–associated germline mutation in MLH1, MSH2, and MSH6.

Women harboring germline mutations in BRCA2 have an increased risk of developing breast and ovarian cancers. The cancers that arise have undergone loss of the wildtype BRCA2 allele, consistent with BRCA2 functioning as a tumor suppressor. The DNA repair defect present in BRCA2-associated cancers renders them highly sensitive to certain classes of DNA damaging agents including platinum agents and PARP inhibitors. BRCA2-mutant cancers have shown acquired resistance to platinum agents through reversion mutations, in which a second mutation in BRCA2 restores an open reading frame that can partially or completely restore functional protein. This kind of functional restoration is often achieved by genomic deletions that excise the exon containing the deleterious germline mutation and place the gene back in frame. Here we report a case of a BRCA2-mutation associated breast cancer that progressed after a prolonged response to PARP inhibitor- based therapy and became chemoresistant. The patient was positive for germline BRCA2 Q2899 * mutation. Next-generation sequencing of the chemoresistant tumor revealed a secondary mutation in BRCA2 that altered BRCA2 Q2899* to Q2899L_converting a non-sense mutation into a missense mutation. In addition to BRCA2 mutation, the tumor had a deletion in MLH1, suggesting that an acquired defect in mis-match repair may have allowed reversion of BRCA2 Q2899* by a point-mutation in this tumor. Analysis of serial specimens from this patient allows reconstruction of the evolution of this tumor, and points to a novel mechanism of reversion mutation due to defects in mismatch repair. This finding suggest how mismatch repair defects can functionally affect BRCA2 mutant cancers, and raise possible therapeutic strategies. Citation Format: JINESH S. GHEEYA, Jeremy Tang, Joseph Ho, Serena Wong, Deborah Toppmeyer, Kim HIrshfield, Lorna Rodriguez, Shridar Ganesan. Identification of reversion mutation by next-generation sequencing in PARP-inhibitor resistant BRCA2 associated breast cancer: Defects in mis-match repair and acquired chemoresistance in breast 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 A81.

350 Background: Lynch syndrome (LS), resulting from a germline mutation in a DNA mismatch repair (MMR) gene, is associated with ~70% lifetime colorectal cancer (CRC) risk. Although LS-associated colon cancer is associated with both favorable prognosis and lack of efficacy to 5-fluorouracil, clinical features of LS-associated rectal cancer (RC) have not been characterized. Methods: Clinical genetics database review (1998–2012) identified all probands with CRC and a deleterious germline mutation in a MMR gene (MLH1, MSH2, MSH6, PMS2) diagnostic of LS. Probands without identifiable mutations or variants of unknown significance were excluded. Clinical history and pedigree was extracted from medical records and Progeny. Results: Of 119 LS patients with CRC, 16 (13.4%) had RC. Mean age at RC diagnosis was 40.6 (range, 23-56) with 31% having synchronous (n=3) or metachronous (n=2) colon cancer. All RC patients met Revised Bethesda and 63% met Amsterdam II criteria. As opposed to LS-associated colon cancer, the majority of RC patients harbored MSH2 mutations (36% colon vs 69% RC, p value 0.01). 11 tumors were analyzed for MSI or defective MMR protein expression by IHC; results were abnormal and thereby concordant with germline test results in all cases. Of 14 RC patients with clinical data, 5 proceeded directly to surgery (4 stage 0/I; 1 stage II). Nine patients received pre-op treatment for clinical stage II/III (n=7) or IV (n=2) disease, with all receiving chemoradiation and five also receiving pre-op FOLFOX. Downstaging of primary tumor occurred in 66.6% (6/9) and of lymph nodes in 77.7% (7/9) of cases. All nine patients underwent R0 resections; however, pCR was not observed in any of the cases. Notably, one patient with clinical T3N+ disease (by MRI and EUS) had upfront surgery identifying pT2N0 disease with prominent tumor infiltrating lymphocytes. Of 14 patients, mean follow-up of 4.3 years (range, 0.3-13.5), none had disease recurrence; however, one was diagnosed with a new primary colon cancer. Conclusions: Although less common than colon cancer,RC is an important component of LS and may be overrepresented in MSH2 mutation carriers. Given high risk of synchronous or metachronous cancers, appropriate surveillance for second malignancies is necessary.