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Breast cancer is a heterogeneous disease. Tumor cells and the surrounding microenvironment form an ecosystem that determine disease progression and response to therapy. To characterize the breast cancer ecosystem and the changes induced by targeted treatment selective pressure, we analyzed 136 HER2-positive tumor samples for the expression of canonical BC tumor diagnostic proteins at a single cell level without disrupting the spatial context. The combined expression of HER2, ER, PR, and Ki67 in more than a million cells was evaluated using a tumor-centric panel combining the four biomarkers in a single tissue section by sequential immunohistochemistry to derive 16 tumor cell phenotypes. Spatial interactions between individual tumor cells and cytotoxic T cells were studied to determine the immune characteristics of the ecosystem and the impact on response to treatment. HER2-positive tumors displayed individuality in tumor cells and immune cells composition, including intrinsic phenotype dominance which only partially overlapped with molecular intrinsic subtyping determined by PAM50 analysis. This single cell analysis of canonical BC biomarkers deepens our understanding of the complex biology of HER2-positive BC and suggests that individual cell-based patient classification may facilitate identification of optimal responders or resistant individual to HER2-targeted therapies.

BACKGROUND: Eribulin is a microtubule-targeting agent approved for the treatment of advanced or metastatic breast cancer (BC) previously treated with anthracycline- and taxane-based regimens. PIK3CA mutation is associated with worse response to chemotherapy in oestrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2−) metastatic BC. We aimed to evaluate the role of phosphoinositide 3-kinase (PI3K)/AKT pathway mutations in eribulin resistance. METHODS: Resistance to eribulin was evaluated in HER2− BC cell lines and patient-derived tumour xenografts, and correlated with a mutation in the PI3K/AKT pathway. RESULTS: Eleven out of 23 HER2− BC xenografts treated with eribulin exhibited disease progression. No correlation with ER status was detected. Among the resistant models, 64% carried mutations in PIK3CA, PIK3R1 or AKT1, but only 17% among the sensitive xenografts (P = 0.036). We observed that eribulin treatment induced AKT phosphorylation in vitro and in patient tumours. In agreement, the addition of PI3K inhibitors reversed primary and acquired resistance to eribulin in xenograft models, regardless of the genetic alterations in PI3K/AKT pathway or ER status. Mechanistically, PI3K blockade reduced p21 levels likely enabling apoptosis, thus sensitising to eribulin treatment. CONCLUSIONS: PI3K pathway activation induces primary resistance or early adaptation to eribulin, supporting the combination of PI3K inhibitors and eribulin for the treatment of HER2− BC patients.

153 Background: Oxaliplatin is a backbone cytotoxic treatment for mCRC patients, particularly in the front-line setting. In the refractory disease, current treatment options are scarce and with limited efficacy. Several retrospective studies have explored the efficacy of oxaliplatin reintroduction/rechallenge (OxRe) in this scenario. However, more evidence is still needed to determine which patients do benefit from this treatment strategy. Methods: The discovery cohort includes all patients treated with oxaliplatin in a third- or fourth-line setting at VHIO between 2015 and 2021 (N = 102). Results were externally validated in a real-world cohort of patients treated at community oncology practices from Oncoclínicas Group in Brazil (N = 157). We analyzed the impact of clinical-molecular features in uni- and multivariable prognostic models in terms of median progression free survival (mPFS) (discovery cohort) and median time to treatment discontinuation (mTTD) (validation cohort). For both cohorts separately, data was extracted from EHRs in structured formats (demographics, tumor characteristics, pharmacy records) and combined with elements from unstructured sources (physician notes on progression and survival status) using technology-based abstraction techniques. Results: In the discovery cohort, 102 out of 735 mCRC patients (13,9%) were eligible. Median oxaliplatin-free interval (from Oxl stop to OxRe) was 17 months (CI95% 13.0-23.2). In OxRe setting, mPFS was 4.0 months (CI95% 3.29-5.03). In PFS multivariate analysis, determinants of favorable outcome were left tumor location (p = 0.01), oxaliplatin-free interval (p = 0.03), administration of Bev in refractory setting (p = 0.001), and not receiving Bev in first-line treatment (p = 0.008). Overall, 27% of all patients had a mPFS > 6 months with OxRe. In the validation cohort, out of 4,317 patients with mCRC, 157 (4%) were treated with OxRe. Median oxaliplatin-free interval was 15 months. Median time to treatment discontinuation (mTTD) of the OxRe was 3.4 months (CI95% 2.8-4.2). In multivariable model, the only independent prognostic factor was addition of Bev to OxRe (p = 0.036). Interestingly, 31% of all patients had mTTD > 6 months, largely enriched (65%) in patients with first Bev exposure at the time of OxRe. Conclusions: This study suggests that in refractory mCRC patients re-exposed to oxaliplatin-based chemotherapy, the addition of Bev is associated with improved outcomes. One-third of the patients are long-term responders (PFS/TTD > 6 months), reinforcing the value of this strategy in selected populations and the relevance of anti-angiogenic agents in refractory mCRC.

Biomarkers; Colorectal cancer; Immunotherapy Biomarcadors; Càncer colorectal; Immunoteràpia Biomarcadores; Cáncer colorrectal; Inmunoterapia The search for immunotherapy biomarkers in Microsatellite Instability High/Deficient Mismatch Repair system (MSI-H/dMMR) metastatic colorectal cancer (mCRC) is an unmet need. Sixteen patients with mCRC and MSI-H/dMMR (determined by either immunohistochemistry or polymerase chain reaction) treated with PD-1/PD-L1 inhibitors at our institution were included. According to whether the progression-free survival with PD-1/PD-L1 inhibitors was longer than 6 months or shorter, patients were clustered into the IT-responder group (n: 9 patients) or IT-resistant group (n: 7 patients), respectively. In order to evaluate determinants of benefit with PD-1/PD-L1 inhibitors, we performed multimodal analysis including genomics (through NGS panel tumour-only with 431 genes) and the immune microenvironment (using CD3, CD8, FOXP3 and PD-L1 antibodies). The following mutations were more frequent in IT-resistant compared with IT-responder groups: B2M (4/7 versus 2/9), CTNNB1 (2/7 versus 0/9), and biallelic PTEN (3/7 versus 1/9). Biallelic ARID1A mutations were found exclusively in the IT-responder group (4/9 patients). Tumour mutational burden did not correlate with immunotherapy benefit, neither the rate of indels in homopolymeric regions. Of note, biallelic ARID1A mutated tumours had the highest immune infiltration and PD-L1 scores, contrary to tumours with CTNNB1 mutation. Immune microenvironment analysis showed higher densities of different T cell subpopulations and PD-L1 expression in IT-responders. Misdiagnosis of MSI-H/dMMR inferred by discordances between immunohistochemistry and polymerase chain reaction was only found in the IT-resistant population (3/7 patients). Biallelic ARID1A mutations and Wnt signalling activation through CTNNB1 mutation were associated with high and low T cell immune infiltrates, respectively, and deserve special attention as determinants of response to PD-1/PD-L1 inhibitors. The non-MSI-H phenotype in dMMR is associated with poor benefit to immunotherapy. Our results suggest that mechanisms of resistance to immunotherapy are multi-factorial. This research was funded by Merck Research Grants (Call 2018) in the Area of Colorectal Cancer Clinical Investigation.

Biomarcadores del cáncer; Cáncer metástico colorrectal; Terapias experimentales Cancer biomarkers; Colorectal metastatic cancer; Experimental therapies Biomarcadors del càncer; Càncer metastàtic colorrectal; Teràpies experimentals Protein biomarkers are widely used in cancer diagnosis, prognosis, and prediction of treatment response. Here we introduce the use of targeted multiplex proteomics (TMP) as a tool to simultaneously measure a panel of 54 proteins involved in oncogenic, tumour suppression, drug metabolism and resistance, in patients with metastatic colorectal cancer (mCRC). TMP provided valuable diagnostic information by unmasking an occult neuroendocrine differentiation and identifying a misclassified case based on abnormal proteins phenotype. No significant differences in protein levels between unpaired primary and metastatic samples were observed. Four proteins were found differentially expressed in KRAS-mutant as compared to wild-type tumours (overexpressed in mutant: KRAS, EGFR; overexpressed in wild-type: TOPO1, TOP2A). Survival analyses revealed the association between mesothelin expression and poor overall survival, whereas lack of PTEN protein expression associated with lower progression-free survival with anti-EGFR-based therapy in the first-line setting for patients with RAS wild-type tumour. Finally, outlier analysis identified putative targetable proteins in 65% of patients lacking a targetable genomic alteration. Our data show that TMP constitutes a promising, novel molecular prescreening tool in mCRC to identify protein expression alterations that may impact on patient outcomes and more precisely guide patient eligibility to clinical trials with novel targeted experimental therapies.

High prevalence of placental-derived complications, such as preeclampsia and intrauterine growth restriction, has been reported in women with breast cancer (BC) treated with chemotherapy during pregnancy (PBC-CHT). Aim: To ascertain whether PBC-CHT is associated with an imbalance of angiogenic factors, surrogate markers for placental insufficiency, that could explain perinatal outcomes. Methods: Prospective study between 2012 and 2016 in a single institution. Soluble fms-like tyrosine kinase (sFlt-1), placental growth factor (PlGF), and soluble endoglin (sEng) in maternal blood were assessed throughout pregnancy in 12 women with BC and 215 controls. Results: Cancer patients were treated with doxorubicin-based regimes and with taxanes. Ten PBC-CHT (83%) developed obstetrical complications. At the end of the third trimester, significantly higher levels of sFlt-1, sFlt-1/PGF ratio, and sEng levels were observed in BC women as compared to controls. Moreover, there was a significant correlation between plasma levels of sFlt-1 and the number of chemotherapy cycles administered. Besides, more chemotherapy cycles correlated with lower birthweight and head circumference at birth. Conclusions: Women with BC treated during pregnancy showed an antiangiogenic state compatible with placental insufficiency. Angiogenic factors could be useful in the clinical obstetric management of these patients, although further studies will be required to guide clinical decision-making.

1061 Background: Molecular characterization of LMBC for the choice of therapy and inclusion in clinical trials is frequently performed in archival biopsies procured several years before. Emerging mut secondary to therapeutic pressure are hence frequently missed but could be detected by real-time analysis of circulating tumor DNA. Aim: 1) To assess the emergence of ERBB2 and other mut upon therapeutic pressure; 2) To compare the concordance of mut in tumor and plasma samples between patients (pts) with metachronous and synchronous sample acquisition. Methods: Pts with LMBC and available tumor biopsy and plasma samples were identified and divided in two groups: 1) Cohort 1 (metachronous) if the time between tissue and plasma acquisition was > 3 months and systemic treatment was given between the sampling; 2) Cohort 2 (synchronous) if sampling occurred with < 3 months interval in the absence of systemic treatment. Tumor and plasma were analyzed using MiSeq Amplicon-based NGS (custom panel of 60 cancer-related genes). The emergent mut in plasma in Cohort 1 and the concordance of ESCAT Tier I and II mut ( PIK3CA, AKT1, ERBB2, ESR1, PTEN) in both Cohorts were determined and correlated with clinical features. Results: 176 pts were included, 112 in Cohort 1 and 64 in Cohort 2. In Cohort 1, emerging mut in PIK3CA were identified in 5 cases (14% of total cases with PIK3CA mut), ESR1 in 22 cases (85% of cases with ESR1 mut) and PTEN in 3 cases (43% of cases with PTEN mut). No emerging ERBB2 or AKT1 mut were seen in plasma. In Cohort 1 ERBB2 mut were identified in 10 pts (8.9%), 5 both in plasma and tissue and 5 only in tissue. Concordance between tumor and plasma was 53% in Cohort 1 and 66% in Cohort 2 (95% CI of the difference -2% to 38%, P =.09). In Cohort 1, concordance was not associated with (neo)adjuvant treatment, number of lines for MBC, presence of visceral metastasis, location of biopsy (primary tumor or metastasis), interval between sampling (range 3.6 – 288 months) or type of systemic treatment before plasma sampling. In Cohort 2, higher concordance associated with shorter interval between primary diagnosis and sampling (p = 0.02). PI3KCA and ESR1 were the two genes most frequently altered in both cohorts. PI3KCA mut had the highest degree of concordance in both groups (70% in Cohort 1 and 76% in Cohort 2). Concordance for ESR1 mut was low in both cohorts (20% and 48%, respectively). Conclusions: A significant number of ESR1 mut emerged upon therapeutic pressure in LMBC. Plasma analysis could also detect the emergence of PIK3CA and PTEN, but not ERBB2 mut. The trend towards lower concordance between metachronous and synchronous tumor and plasma sampling is probably due to increased tumor heterogeneity and clonal diversity secondary to systemic treatment. Our findings confirm that liquid biopsies provide complementary information respect to tumor tissue that may be potentially useful for clinical decisions.

1086 Background: Genomic alterations driving MBC progression may be better captured by ctDNA reflecting clonal evolution, but it is currently unknow whether ctDNA analysis can replace tumor sequencing for clinical decision purposes. Aim: to study the concordance between mut in synchronous plasma and tumor samples prospectively collected from patients (pts) with MBC progressing on their last systemic therapy. Methods: MiSeq Amplicon-based NGS (custom panel of 60 cancer-related genes; BRCA1/2 and PALB2 not included) was performed in both tumor biopsy and plasma. The concordance of ESCAT Tier I and II mut ( PIK3CA, AKT1, ERBB2, ESR1, PTEN) was determined and correlated with mutant allele fraction (MAF), TDV, and clinical features. Findings from liquid biopsies were classified as true positive (TP-ctDNA) if a given mut was detected in both tumor and plasma and false negative (FN-ctDNA) if only in the tumor. TDV: all metastasis volume assessed by CT scan (excluding sclerotic bone metastasis), and analyzed by an experienced radiologist using the 3DSlicer semiautomatic segmentation tool (TDV = pixel size x number of pixels). Non-shedding cases were those where any mut was detected in tumor but none in plasma. Results: 88 cases were collected (luminal 64, HER2+ 17, triple negative 7). Median age at diagnosis 49 years (range 28-80). Radiomics assessment could be performed in 78/88 cases. The plasma/tissue concordance at case level was 74%. Discordance came from 23 cases; in 15 cases mut was only found in tissue and in 8 cases it was only detected in plasma. At gene level, PIK3CA had the highest concordance (79%); in ESR1 it was 52%. Higher concordance associated with non-luminal subtype (OR 0.08, 95%CI 0.002 – 0.59) and shorter interval between primary diagnosis and metastatic relapse (20.3 vs 51 months; p =.02), but not with MAF. FN-ctDNA occurred in 15/49 cases (31%) and associated with luminal subtype (p =.02), but not with other clinical variables. Non-shedding cases associated with older age (p =.03), luminal subtype (p =.007), low TDV (p =.0006) and < 3 metastatic sites (p =.05). In patients with visceral metastasis (n = 45), higher TDV associated with lower probability of FN-ctDNA (p =.03). All non-luminal subtypes were shedders and all but one were TP-ctDNA. In multivariate analysis, higher probability of TP-ctDNA in luminal tumors associated with tumor sampling from a progressing lesion (OR 10.8; 95% 1.5 – 122; p =.03) and shorter interval between diagnosis of metastatic disease and biopsy (OR 0.96, 95% CI 0.92 – 0.99; p =.03). Conclusions: Our results suggest that ctDNA can detect a significant proportion of clinically relevant mut in MBC. Patients’ characteristics, tumor subtype, type of gene, and tumor volume should be integrated with ctDNA results to better inform clinical decisions.

Fusobacterium nucleatum; Càncer de recte avançat local; Quimioteràpia preoperatòria Fusobacterium nucleatum; Cáncer de recto avanzado local; Quimiorradioterapia preoperatoria Fusobacterium nucleatum; Locally advanced rectal cancer; Preoperative chemoradiotherapy Background Accumulating evidence has identified Fusobacterium as an important pathogenic gut bacterium associated with colorectal cancer. Nevertheless, only limited data exist about the role of this bacterium in locally advanced rectal cancer (LARC). In this study, we quantified Fusobacterium nucleatum in untreated and post-neoadjuvant chemoradiotherapy (nCRT) samples from LARC patients and investigated its association with therapy response and survival. Patients and methods A total of 254 samples from 143 patients with rectal adenocarcinomas were analyzed for the presence and abundance of F. nucleatum using RNA in situ hybridization and digital image analysis. Assay accuracy was determined using infected cell lines and tumor samples with available quantitative PCR data. We studied the impact of F. nucleatum load on pathologic complete response and relapse-free survival. Treatment-induced changes were evaluated in paired pre- and post-nCRT samples (n = 71). Finally, tumor microenvironment changes during nCRT were assessed in paired samples (n = 45) by immune contexture analysis. Results F. nucleatum tissue levels by RNA in situ hybridization strongly correlated with quantitative PCR (r = 0.804, P < 0.001). F. nucleatum abundance was higher in untreated [median, 7.4; 95% confidence interval (3.7–16.2)] compared with treated [median, 1.6; 95% confidence interval (1.3–2.4)] tumors (P

Oncologia de precisió; Assaigs clínics; Preselecció molecular Oncología de precisión; Ensayos clínicos; Preselección molecular Precision oncology; Clinical Trials; Molecular prescreening Most academic precision oncology programs have been designed to facilitate enrollment of patients in early clinical trials with matched targeted agents. Over the last decade, major changes were seen both in the targetable molecular alteration landscape and in drug development trends. In this article, we describe how the Vall d’Hebron Institute of Oncology molecular prescreening program adapted to a dynamic model of biomarker-drug codevelopment. We started with a tumor-agnostic hotspot mutation panel plus in situ hybridization and immunohistochemistry of selected markers and subsequently transitioned to tumor-specific amplicon-based next-generation sequencing (NGS) tests together with custom copy number, fusion, and outlier gene expression panels. All assays are optimized for archived formalin-fixed paraffin-embedded tumor tissues without matched germline sequencing. In parallel, biomarker-matched trials evolved from a scenario of few targets and large populations (such as PI3K inhibitors in PIK3CA mutants) to a complex situation with many targets and small populations (such as multiple targetable fusion events). Recruitment rates in clinical trials with mandatory biomarkers decreased over the last 3 years. Molecular tumor board meetings proved critical to guide oncologists on emerging biomarkers for clinical testing and interpretation of NGS results. The substantial increase of immunotherapy trials had a major impact in target prioritization and guided clinical implementation of new markers, such as tumor mutational burden, with larger exon-based NGS assays and gene expression signatures to capture microenvironment infiltration patterns. This new multiomics era of precision oncology is expected to increase the opportunities for early clinical trial matching.

INTRODUCTION: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic raises many questions about the management of patients with significant comorbidities. Hematologic patients are usually fragile due to an important immunosuppression, so the impact of coronavirus disease (COVID-19) is yet to be determined. MATERIALS AND METHODS: We conducted a single-center retrospective observational study of patients with hematologic malignancies diagnosed with SARS-CoV-2 at Vall d´Hebron University Hospital (HUVH) between March 1st and May 31st 2020 to analyze their clinical characteristics and evolution. Patient's demographic data, underlying pathology, signs and symptoms of COVID-19, treatment received and clinical course were collected. A statistical analysis was performed to identify the possible variables associated with COVID-19 mortality. For this purpose, we used univariate and multivariable logistic regression models. RESULTS: We identified 70 patients with PCR confirmed SARS-CoV-2 infection and hematologic malignancy. The median age was 75 years (range 22-91), and 44% were female. The majority (74%) had evidence of active malignancy and 53% were receiving active therapy. Lymphoid pathology (73%) predominated over myeloid. The median number of previous lines of treatment was 0 (range 0-6), 23% had received at least 2 lines, whereas 10% underwent hematopoietic stem cell transplantation (HSCT) (5 patients allo-HSCT, 2 auto-HSCT). Half of the patients had more than one pre-existing comorbidity (17% obstructive pulmonary disease). At diagnosis the most common symptoms were fever (76%), cough (60%) and dyspnea (31%). We observed that 58% of patients presented a chest X-ray compatible with COVID-19. Regarding laboratory parameters, stood out lymphopenia (65% of patients presented COVID-19 was acquired via nosocomial infection in 23% of patients, 91% of them requiring hospitalization, 14% in the Intensive Care Unit (ICU). The median days of hospitalization since diagnosis was 17 (range 3-55). The case fatality rate (CFR) from COVID-19 was higher in hematologic patients than the one observed in non-hematologic patients at the HUVH (figure 1), being of 41% at 11 days from diagnosis. CFR was higher in patients older than 75 years old (61%), while the mortality among patients receiving active therapy was 42%. The main cause of death was acute respiratory failure (93%). In the univariate logistic regression model, age >75 years (OR 1.07; p=0.008), active malignancy (OR 5; p=0,02), >1 comorbidity (OR 5.3; p=0,049) and high levels of IL-6 (OR 8.2; p= 0.005) were statistically significant. In the multivariable logistic regression model, age ≥75 years (OR 4.4; p=0.01) and IL-6 levels at baseline > 59.6 pg/mL (OR 7.2; p=0.01) were associated with a higher mortality (table 1). The presence of an active malignancy was not a significant variable in the multivariable logistic regression model. CONCLUSIONS: Patients with hematologic malignancies and COVID-19 presented similar symptoms, signs and radiological characteristics to those described in the general population at diagnosis. In our cohort, advanced age and high IL-6 values were associated with higher mortality. Furthermore, it was observed that active hematologic disease is a factor of poor prognosis of COVID-19. Disclosures Salamero: Daichii Sankyo:Honoraria;Celgene:Consultancy, Honoraria;Novartis:Consultancy, Honoraria;Jazz Pharmaceuticals:Consultancy, Honoraria;Pfizer:Consultancy.Abrisqueta:Janssen:Consultancy, Honoraria, Speakers Bureau;AbbVie:Consultancy, Honoraria, Speakers Bureau;Roche:Consultancy, Honoraria, Speakers Bureau;Celgene:Consultancy, Honoraria.Bosch:Hoffmann-La Roche:Research Funding.

Colorectal cancer; Driver gene; Mutant allele fraction Càncer colorectal; Gen conductor; Fracció d'al·lel mutant Cáncer colorrectal; Gen conductor; Fracción de alelo mutante Sequencing of tumors is now routine and guides personalized cancer therapy. Mutant allele fractions (MAFs, or the 'mutation dose') of a driver gene may reveal the genomic structure of tumors and influence response to targeted therapies. We performed a comprehensive analysis of MAFs of driver alterations in unpaired primary and metastatic colorectal cancer (CRC) at our institution from 2010 to 2015 and studied their potential clinical relevance. Of 763 CRC samples, 622 had detailed annotation on overall survival in the metastatic setting (OSmet) and 89 received targeted agents matched to KRAS (MEK inhibitors), BRAF (BRAF inhibitors), or PIK3CA mutations (PI3K pathway inhibitors). MAFs of each variant were normalized for tumor purity in the sample (adjMAFs). We found lower adjMAFs for BRAFV600E and PIK3CA than for KRAS, NRAS, and BRAF non-V600 variants. TP53 and BRAFV600E adjMAFs were higher in metastases as compared to primary tumors, and high KRAS adjMAFs were found in CRC metastases of patients with KRAS wild-type primary tumors previously exposed to EGFR antibodies. Patients with RAS- or BRAFV600E -mutated tumors, irrespective of adjMAFs, had worse OSmet. There was no significant association between adjMAFs and time to progression on targeted therapies matched to KRAS, BRAF, or PIK3CA mutations, potentially related to the limited antitumor activity of the employed drugs (overall response rate of 4.5%). In conclusion, the lower BRAFV600E and PIK3CA adjMAFs in subsets of primary CRC tumors indicate subclonality of these driver genes. Differences in adjMAFs between metastases and primary tumors suggest that approved therapies may result in selection of BRAFV600E - and KRAS-resistant clones and an increase in genomic heterogeneity with acquired TP53 alterations. Despite significant differences in prognosis according to mutations in driver oncogenes, adjMAFs levels did not impact on survival and did not help predict benefit with matched targeted agents in the metastatic setting.

1075 Background: NGS in ctDNA from MBC is feasible and results may be informative for patients’ management, especially in non-luminal tumors (Oliveira et al, ASCO 2018). We aimed to study the determinants of concordance in CRG in a cohort of 60 MBC patients undergoing tBx and ctDNA collection. Methods: MiSeq Amplicon-based NGS (59 cancer-related genes) was performed in one single metastatic lesion per patient and compared with liquid biopsies taken at the same time point at disease progression to prior treatment. The concordance in CRG ( PIK3CA, AKT1, ERBB2, ESR1, PTEN, BRAF, FGFR1, HRAS, KRAS, and PIK3R1) in tBx vs ctDNA was determined at patient and at mutation (mut) level and correlated with mutant allele fraction (MAF), total disease volume (TDV), and clinical characteristics. True positive in plasma (TPP): patient with a mut detected both in ctDNA and tBx. TDV was defined as all metastasis volume assessed by CT scan (excluding sclerotic bone metastasis), and analyzed by an experienced radiologist using the 3DSlicer semiautomatic segmentation tool (TDV = pixel size x number of pixels). Results: Concordance in CRG at patient and mut level was 72% and 55%, respectively. Concordance for ERBB2 (1/1; 100%) and PIK3CA (17/22; 77%) was higher than for ESR1 (8/20; 40%) and AKT1 (2/6; 33%). ctDNA failed to detect 14 mut present in tBx ( ESR1 n = 5, PIK3CA n = 5, AKT1 n = 3, BRAF n = 1). Concordance was 100% for non-luminal and 60% for luminal cases (P = 0.01). In univariate analysis, concordance was not associated with MAF in tBx (P = 0.15), TDV (p = 0.86), number of prior lines of therapy (P = 0.57), number of metastatic sites (P = 0.56) or presence of visceral metastasis (P = 1.0). In patients with PIK3CA mut (N = 22), those with TPP had a numerically higher TDV than those where a PIK3CA mut was not detected in ctDNA (20.9cm3 vs 5.1cm3, P = 0.28). Across all patients, in the multivariate logistic model adjusted for other factors, TDV was a determinant of TPP (OR 1.02, 95%CI 1.0-1.06; P = 0.059). For each increase of 1cm3 in TDV, there was a 2% increase in the probability of detecting a mut in ctDNA. Conclusions: Our results suggest that liquid biopsy testing for the detection of actionable CRG is clinically valid in MBC, although its yield depends on several factors – tumor subtype, analyzed gene, and possibly tumor volume – that reflect both tumor heterogeneity and tumor shedding rate. Due to the potential clinical implications, the observation that mutation detection in ctDNA may correlate with tumor volume merits further study in a larger dataset.

1073Background: Next generation sequencing (NGS) of tBx is the basis for precision medicine. Most tBx used for NGS are archival primary tumors, often acquired several years before starting matched ...

5569 Background: Aberrant PI3K/AKT/mTOR activation is common in GYN. Predictive biomarkers to PAMi in GYN have yet to be identified. Methods: Advanced GYN pts with available genomic data, treated with PAMi in phase I/II clinical trials were selected. Mutation (mut) allele fractions (MAFs) were corrected for tumor purity and defined as clonal (cl) (≥ 0.4) or subclonal (scl) ( < 0.4). PAMi efficacy: (i) time to progression (TTP); (ii) clinical benefit rate (CBR: complete/partial response or stable disease > 4 months [m]); and (iii) ratio TTP on PAMi/ TTP on non-standard chemotherapy pre- or post-PAMi (PAMi/nsChemo TTP). Results: From 2010 to 2016, 264 GYN pts (152 ovarian(OC); 75 endometrial(EC); 37 cervical(CC)) had genomic analysis; 50 pts (24 OC [11 PIK3CA mut, 5 KRAS mut], 15 EC [6 PIK3CA mut, 5 PTEN mut, 4 KRAS mut], and 11 CC [9 PIK3CA mut, 3 KRAS mut]) received PAMi (17 pan-PI3K/mTOR or AKT inh, 17 α-PI3K inh, 16 PAMi targeted combos). PAMi therapy was matched (MA) to PIK3CA/PTEN mut in 30 pts (60%). Median age was 57 years (30-70); median number of prior lines was 2 (1-6) and 34 pts (68%) received nsChemo. Efficacy of PAMi: (i) median TTP (3.27 m [95% CI 2.1-4.4] with trend for longer TTP in OC compared to others [3.93 vs. 2.1 m, HR 0.57; p = 0.08], without differences according to MA status [p = 0.26] or regimen [p = 0.5]); (ii) CBR (42% [95% CI 27-58%], without differences according to tumor type [p = 0.47], MA status [p = 1] or regimen [p = 0.86]); and (iii) TTP PAMi/nsChemo ≥ 1.3 (42% [95% CI 24-63%], without differences according to tumor type [p = 0.53], MA status [p = 0.23] or regimen [p = 0.41]). Partial responses were seen in 5 pts (4 PIK3CA mut on single agent PAMi; 1 KRAS mut on PI3K + MEK inh). Of 4 KRAS mut pts, none had CBR with single agent PAMi. PIK3CA mut were cl in 63% of OC, 17% of EC and 40% of CC. Clonal exon 20 PIK3CA mut were more frequent in OC (p = 0.03). We found longer TTP for cl PIK3CA events (4.0 vs. 1.5 m in scl, HR 5.1, p = 0.006) and a trend for exon 20 events (4.4 vs. 1.4 m in exon 9, HR 1.7, p = 0.25). Conclusions: Regardless of PIK3CA/PTEN mut status, PAMi confer CBR in almost 40% of GYN pts. Functionality and clonality of PIK3CA mut impact on TTP and interact with tumor type. Coexisting KRAS mut may drive resistance to single agent PAMi.

2581 Background: Several FGFR and ligand (11q) alterations have been described in cancer. While FGFR fusions are recognized biomarkers of response to FGFRinh, it is still unclear to what extent FGFRamp, FGFR mRNA high expression (mRNAh) or FGFRmut predict sensitivity in the clinic. Methods: Retrospective analysis of pts with molecularly-selected FGFRamp/mRNAh/mut tumors treated with FGFRinh in phase 1 trials at our institution. Mut were detected with IlluminaÒ or Foundation OneÒ. FGFR1-2amp were analyzed by in situ hybridization and mRNA levels by qRT-PCR or nCounterÒ. Clinical benefit (ClinBen) was defined as any tumor shrinkage plus disease control for ³ 4 months (m). Time to progression (TTP) was defined as time between start of FGFRinh and end for any cause. Results: From 2011 to 2016, 36 pts with FGFRamp(25)/mRNAh(5)/mut(6) received an FGFRinh (irreversible- [11 cases (c)] or reversible-FGFR1-4inh [23 c], isoform-specific FGFRinh [3 c] or combo with PI3Kinh [1 c]). Median age 55 yrs (34-76); median prior palliative lines was 3 (0-8); tumor types: breast (17), colorectal (3), esophagus (3), liver (3), lung (3), others (7). Median TTP was 1.67 m (CI 95%; 1.40-2.87). In the FGFRamp/mRNAh population (30), 7 pts achieved ClinBen (23%). 4 out of these seven pts had mRNAh (1 FGFR2amp breast with FGFR2 mRNAh, 1 bladder FGFR3 mRNAh and 2 liver FGFR4 mRNAh without known amp), and 2 pts harboured 11q co-amplification (1 FGFR2amp breast, 1 FGFR2amp head and neck). There was no correlation between ClinBen and level of FGFRamp in the overall population (p = 0.51) or in the breast cancer group (p = 0.29). Of 6 FGFRmut pts, one with bladder cancer had ClinBen (clonal oncogenic FGFR3 S249C). The remaining 5 unresponsive FGFRmut pts had subclonal events, some of these FGFRmut were of unknown functional significance, and had coexisting oncogene mut in MAPK or PI3K pathways. Conclusions: Our results suggest that ClinBen with FGFRinh in the FGFRamp setting is enriched in pts with high mRNA expression and/or ligand co-amplification, and in the FGFRmut population may be dependent on clonality and functionality of the event and co-existence of driver mut.

6031 Background: Multiple genomic alterations were described in HNC, including squamous cell carcinomas (SCC), salivary gland (SG) and nasopharyngeal (NF) tumors. Tumor molecular profiling (TMP) may increase therapeutic alternatives in early trials for pts with refractory metastatic (met) HNC. We evaluate the impact of matched/unmatched therapy (mT/uT) in HNC with potentially targetable alterations. Methods: From 2010-16, 47 met HNC pts were treated in 57 early trials after TMP. Clinical benefit was measured by: time to progression (TTP); clinical benefit rate (CBR: complete response [CR], partial response [PR] and stable disease [SD] > 4months [m]); progression-free survival [PFS] ratio≥1.3 (PFS under molecular therapeutics/PFS upon last prior chemotherapy [pT]). Results: Median age was 51 years; median number of pT lines was 1 (0-5). In total, 26 SCC, 11 SG, 8 NF and 2 nasosinusal pts (mostly with lymph nodes and lung met) were treated with small kinases (SK) inhibitors (inh) (50%; main targets PI3K/HER/FGFR), immune-oncology (IO) drugs (40%, PD-1/PD-L1), angiogenesis inh (5%) or chaperone, cytidine analog, RNA polymerase (5%). 14/57 trials were mT including CDKinh (1 CDKN2A mutation [mut]), PI3Kinh (5 PIK3CA mut, 2 PTEN mut), PI3K/MEKinh (1 NRAS mut), HERinh (1 ERBB3mut), FGFRinh (2 FGFR1mRNA high, 1 FGF3/4/19 ligand amplified) and porcupine inh (1 ZNFR3mut). Distribution by tumor: IO (16 SCC/5 NF), SKmT (8SG/4SCC/2NF) and SKuT (9SCC/4SG). Responses: 1CR in SCC (IO), 5 PR in SCC (4 IO, 1 FGFRinh), 3 PR in NF (1 cytidin analog, 1 IO, 1 PI3K/MEKinh). Benefit: median TTP 9.33m (CI95% 7-20) with upward trend in NF and SG vs SCC (HR 0.6;p = 0.28), without differences according to target therapies (HR 0.8; p = 0.9); CBR of 58%, without differences by tumor type (p = 0.42) or therapy (SKmT, SKuT, IO; p = 0.5); 60% with PFS ratio≥1.3, significantly higher in SCC and SG (p = 0.016), particularly with IO drug and SKmT, respectively. Conclusions: Considering our preselected fit population as bias selection, individualized treatment selection with novel therapeutics based on TMP, especially in NF and SG irrespective of targets (SKmT, SKuT, IO), and in SCC with IO drugs, seems to confer substantial clinical benefit.

Malignitats ginecològiques; Fracció al·lel mutant; PI3K Neoplasias ginecológicas; Fracción alélica mutante; PI3K Gynecologic malignancies; Mutant allele fraction; PI3K Objectives Aberrant PI3K/AKT/mTOR activation is common in gynaecological malignancies. However, predictive biomarkers of response to PI3K pathway inhibitors (PAMi) have yet to be identified. Methods We analysed the outcomes of patients with advanced gynaecological cancer with available genomic data, treated with PAMi as single agents or in combination in phase I clinical trials. Clinical relevance of the PIK3CA mutant allele fraction (MAF) was investigated. MAF of each variant was normalised for tumour purity in the sample (adjMAFs) to infer clonality of PIK3CA mutations, defined as clonal (≥0.4) or subclonal (