Germline and somatic DNA damage repair gene mutations potentially predict the efficacy of relevant treatment in Chinese patients with pancreatic ductal adenocarcinoma.

e16732 Background: PDAC is a fatal disease with molecular heterogeneity, inducing differences in biological behaviour and therapeutic strategy. We conducted a study to reveal the mutation landscape of Chinese PDAC patients, and investigate the predictive role of germline and somatic DNA damage repair (DDR) status in precise treatment. Methods: 195 PDAC patients were enrolled from multiple medical centers of China between Jan 2016 to Nov 2019. Baseline clinical or genetic characteristics, and survival status were collected. NGS were performed on paraffin-embedded resected tissues or peripheral blood using a panel of 417 genes, including 50 DDR-related genes. Survival analysis was conducted using Kaplan-Meier, and Cox proportional hazard regression model. Results: The main driver genes were KRAS, TP53, CDKN2A, and SMAD4. Patients with KRAS mutation showed worse OS than those without (p = 0.048). DDR deficiency were identified in 15.38% of overall patients, mainly occurred in BRCA2 (4.62%), ATM (4.10%), RAD50 (1.54%) and MLH1 genes (1.03%). No significant improvement of OS existed between patients with or without DDR mutations (p = 0.88). Treatment with olaparib (adjusted HR, 0.2550; P = 0.0720) or platinum-based chemotherapy (adjusted HR, 0.1308; P = 0.0185) respectively decreased hazard of death in patients with DDR mutation. Besides BRCA gene, ATM mutant patients treated with olaparib harbored prolonged median OS than those without olaparib treatment (22.25 vs 15.2 month). Despite a little higher PD-L1 expression rate were seen in DDR mutant patients (29.17% vs 20.51%), no statistical correlation between tumor mutation burden level and DDR mutation was identified. And in patients treated with PD-1 blockade, 2 patients of DDR wild-type group both had SD, whereas of the remaining 5 patients with DDR deficiency, 1 was evaluated as PR, 3 as SD, and 1 as PD (ORR, 0 wt vs 20% mut). Conclusions: In this multi-center retrospective study, we deciphered the intra-tumoral genetic heterogeneity in Chinese PDAC population, which differs from western patients cohort to some extent. We found the potential role of germline and somatic DDR mutation status in predicting the response to olaparib and platinum-based chemotherapy, especially with BRCA or ATM mutation. However, DDR alteration was limited in prediction of hypermutational status and sensitivity to PD-1 blockade. Our study may provide a valuable evidence for clinical application of DDR mutation as a potential biomarker for precise treatment.