Impact of DNA damage repair alterations on real-world response to therapy in metastatic colorectal cancer.

e15557 Background: Alterations in the DNA damage repair (DDR) pathway genes contribute to tumor development. These alterations can be exploited by cytotoxic chemotherapy regimens that induce DNA damage. Platinum chemotherapy agents have been shown to be particularly effective in breast and ovarian cancer patients with alterations in the DDR pathway. However, the clinical impact of DDR alterations in metastatic colorectal cancer (mCRC) is still poorly understood. In this study, we utilize a large national database to evaluate clinical outcomes in patients with mCRC and alterations in DDR pathway genes. Methods: We reviewed 5602 patients that received standard fluorouracil based first-line chemotherapy regimens for mCRC using the nationwide Flatiron Health EHR-derived de-identified database. Chemotherapy regimens were categorized as a platinum-based doublet (FOLFOX, CAPOX), irinotecan-based doublets (FOLFIRI), or triplet (FOLFOXIRI). Overall survival (OS) was summarized within groups via Kaplan-Meier survival estimates. OS was compared between groups in the context of univariable and multivariable Cox proportional hazards models controlling for age, gender, DDR status, stage at diagnosis, ECOG, RAS/RAF status, MMR status, albumin and CEA at diagnosis. OS was defined as the time in months between date of first line therapy initiation to death. Results: DDR gene alterations were indentified in 35.7% (2001) patients.The most frequent mutations were in ATM (13.3%) and BRCA2 (8.3%). There was no significant difference in OS based on DDR mutation status. Within DDR altered patients, there was no difference in OS between those who received a platinum-based doublet, irinotecan-based doublet or triplet first-line therapy. Time to next treatment or death (TTNTD) was significantly improved with an irinotecan-containing doublet regimen and triplet regimen compared to a platinum-based doublet in a multivariable model (HR 0.79, p = 0.001 and HR 0.68, p = 0.002, respectively). There was no difference in OS in DDR-mutated patients that received an irinotecan-based regimen in the first line followed by an oxaliplatin-based regimen in the second line or the reverse sequence. When evaluating the impact of commonly co-mutated genes on survival we observed a worse OS in patients with a KRAS mutation in addition to a DDR mutation (HR 1.19, p = 0.045). An APC mutation was associated with an improved OS in the entire cohort, regardless of DDR status (HR 0.76, p < 0.001). Conclusions: In this real-world population, approximately one third of patients with mCRC harbored an alteration in a DDR pathway gene. In these patients, TTNTD was greater with irinotecan-containing first line therapies (doublet or triplet). However, OS was similar regardless of which first-line chemotherapy was used.