Comprehensive genomic analysis for homologous recombination deficiency in pancreatic cancer

e15168 Background: Although homologous recombination deficiency (HRD) has been heavily studied in oncology, HRD in pancreatic cancer remains poorly understood beyond germline alterations in BRCA1, BRCA2 and PALB2. Methods: We performed whole exome sequencing (WES) on 205 patients with pancreatic cancer. Germline and somatic mutations in HRD genes were evaluated: (1) canonical HRD mutation ( BRCA1, BRCA2 and PALB2); and (2) non-canonical HRD mutation ( ATM, ATR, ATRX, CHEK2, BAP1, BARD1, BLM, BRIP1, NBN, RAD51 genes, RAD54 genes, FANC genes and ERCC genes). In addition, signature-based HRD classifiers were also applied: (1) the genomic instability score (GIS); (2) substitution base signature 3 (SBS3); and (3) small insertion and deletions 83B (ID83B). The frequency of HRD mutations and signatures-based HRD in pancreatic cancer were evaluated and their clinical utility were assessed by confirming the association with the response to platinum-containing chemotherapy. Results: Among the 205 patients, 41 patients (20.0%) were identified to harbor HRD mutations. Germline and somatic HRD mutations were identified in 19 (9.3%) and 24 (11.7%) patients, respectively. Mutations in canonical genes and non-canonical genes were found in 12 (5.9%) and 37 (18.1%) patients, respectively. Using signature-based HRD classifier, additional 45 (22.0%) patients were determined to be HRD. Among patients who received first-line FOLFIRINOX ( N = 113), canonical HRD mutation and signature-based HRD group showed higher response rate than non-canonical HRD and non-HRD group (75.0% and 57.1% vs. 31.3% and 33.3%, respectively). In the survival analysis of patients treated with FOLFIRINOX, canonical HRD and signature-based HRD group tended to have better overall survival than non-HRD group. Conclusions: Comprehensive genomic analysis could identify a significant number of HRD pancreatic cancer beyond germline BRCA1,2 and PALB2 mutation, and it would be helpful to choose the appropriate chemotherapy regimen.