Homologous recombination deficiency (HRD) in patients with pancreatic cancer (PC) and response to chemotherapy.

Abstract

317 Background: Mutations or copy number abnormalities of genes involved in homologous recombination occur in PC. DNA-based measures of HRD have been developed and may help identify tumors with better response to DNA damaging agents. This study aimed to describe the mutation and HRD status of PC and determine their association with treatment response and outcome. Methods: This was a retrospective analysis of tumor samples from patients treated at Indiana University for locally advanced or metastatic PC. Patients were included if they received gemcitabine/nab-paclitaxel or FOLFIRINOX and had adequate follow up to assess survival and response to therapy. Tumor analysis generated a 3-biomarker (LOH, TAI, LST) HRD score and mutation data for 45 genes. Results: Ninety-one samples met inclusion criteria, 78 (15 FFPE and 63 FNA) generated mutation data. HRD analysis was successful for 57; the primary cause of failure low tumor %. The final analysis set consisted of 78 samples with mutation status, including 57 with HRD scores (range= 5 -61 (median=18,)). Six BRCA1/ 2 mutations were detected, 5 had high HRD scores, with 4 in the top decile (p=0.011). Other DNA repair gene mutations ( ATM=3, ATR=1, BRIP1=1 and FANCI=1) were detected, but most retained one functional allele and were not associated with HRD score. There was no statistically significant correlation between HRD score and response to FOLFIRINOX (OR per interquartile range = 1.40, p=0.32 adjusted for treatment). HRD score was not associated with PFS or OS. For FOLFIRINOX, median survival times for low vs. high HRD (dichotomized at the median) were 5.3 vs. 9.4 months PFS (p=0.049) and OS 12.3 vs. 11.3 months (p=0.89). For gemcitabine/nab-paclitaxel, mPFS was 6.1 vs. 4.6 months (p=0.88), and mOS was 14.4 vs. 11.4 months (p=0.29). Conclusions: Mutations in DNA repair genes occur in PC, and HRD scores can be generated in the majority of cases. HRD score was not significantly associated with higher response rate or prolonged survival in relation to FOLFIRINOX in this small non-randomized retrospective cohort. Larger studies to examine the association of mutations in DNA repair genes and HRD may be needed to detect significant associations.