Comprehensive tumor profiling reveals unique molecular differences between peritoneal metastases and primary colorectal adenocarcinoma

Background and Objectives: Peritoneal metastases (PM) from primary colorectal cancer (pCRC) are associated with poor outcomes; however, molecular differences are not well defined. Methods: We compared unpaired tumor profiles of patients with pCRC and PM from Caris Life Sciences. Testing included next-generation sequencing of 592 genes, microsatellite instability (MSI) and tumor mutational burden (TMB). Mutations were test-defined as pathogenic (PATH). Results: Six hundred seventeen pCRC and 348 PM patients had similar gender (55% male) and age (median 59). PATHs were similar between PM and pCRC in KRAS, BRAF, SMAD2, SMAD4, and PTEN. pCRC PATHs were increased in APC (76% vs 48%, P <.01), ARID1A (29% vs 12%, P <.05), TP53 (72% vs 53%, P <.01), PIK3CA (22% vs 15%, P <.05), and FBXW7 (13% vs 7%, P <.01) compared with PM. Mucinous PM had more PATHs in GNAS (19% vs 8%, P =.032) while nonmucinous PM had more PATHs in BRAF (13% vs 8%, P =.027). Right-sided PM had decreased PATHs in APC (39% vs 68%, P <.0001), ARID1A (7% vs 38%, P <.004), and TP53 (48% vs 65%, P =.033) while there were no difference for left-sided PM. Nine percent of pCRC and 6% of PM were MSI-high (P = NS). There was no difference in TMB-high, TMB-intermediate, or TMB-low between PM and pCRC. Conclusions: PM have similar rates of KRAS mutation with increased PATHs in GNAS (mucinous) and BRAF (nonmucinous) compared to pCRC. No differences in MSI or TMB were identified between PM and pCRC tumors. These findings inform future study into the molecular profile of PM.