Spectrum of Response to Platinum and PARP Inhibitors in Germline BRCA Associated Pancreatic Cancer in the Clinical and Pre-clinical Setting

Germline BRCA-associated pancreatic ductal adenocarcinoma(glBRCA-PDAC) tumors aresusceptible to platinum/PARP-inhibition. The clinical outcomesof 125 glBRCA-PDAC patients was stratified based on the spectrum of response to platinum/PARP-inhibition: i)Refractory(OS<6 months) ii)Durable response followed by acquired-resistance(OS<36 months); iii)Long-term responders(OS>36 months). Patient-derived-xenografts(PDX) were generated from 25 glBRCA-PDAC patients at different clinical time-points. Response to platinum/PARP-inhibition in-vivo and ex-vivo culture(EVOC) correlated with clinical response. We deciphered the mechanisms of resistance in glBRCA-PDAC and identified homologous recombination(HR)-proficiency and secondary-mutations restoring partial functionality as the most dominant resistant mechanism. Yet, a subset of HR-deficient(HRD) patients demonstrated clinical resistance. Their tumors displayed basal-like molecular subtype and were more aneuploid. Tumor-mutational-burden(TMB) was high in HRD-PDAC and significantly higher in tumors with secondary mutations. Anti-PD1 attenuated tumor growth in a novel humanized glBRCA-PDAC PDX-model. This work demonstrates the utility ofpreclinicalmodels, including EVOC, to predict response of glBRCA-PDAC to treatment, whichhas potential to inform time-sensitive medical decisions. To investigate thee expression patterns of our BRCA PDAC PDX models we sequenced PDX models with 1-3 biological replicates (i.e. different xenograft generaition in mice).