Molecular comparison of primary colorectal cancer (pCRC) with peritoneal metastases (PM).

Abstract

498 Background: PM from CRC are associated with poor outcomes; however, molecular differences are not defined. Methods: We compared tumor profiles of pCRC and PM patients (pts) from Caris Life Sciences. Testing included next-generation sequencing (NGS) of 592 genes, immunohistochemistry (IHC), copy number variants (CNV), microsatellite instability (MSI) and tumor mutational burden (TMB). Mutations were termed pathogenic (PATH) or variants of undetermined significance (VUS). TMB in mutations/Mb (MMB) was compared. Results: 617 pCRC and 348 PM pts had similar gender (55% male) and age (median 59). 232 pCRC were left-sided (LS), 189 right-sided (RS), 147 rectum (R) and 49 not otherwise specified (NOS); PM were 45 RS, 29 LS, 22 R and 252 NOS. For pts with IHC testing, expression was increased in PM in TOPO1 (62% v. 52%, p < 0.01), ERCC1 (27% v. 18%, p < 0.01) and MLH1 (96% v. 92%, p < 0.05) and decreased in PD-1 (36% v. 65%, p < 0.01), TOP2A (76% v. 100%, p < 0.01) and PTEN (64% v. 72%, p < 0.05). By sidedness, LS PM were more frequently TOP01 and PD-L1 and less commonly MGMT positive compared to pCRC. PTEN IHC was higher in R pCRC than PM. 7 CNVs were increased in PM ( ADGR2A2, CCND1, ELL, FGF3, FGF4, JAK3 and PDGFRB) and FLT3 CNVs were decreased. MYC CNVs were more common in RS PM compared to pCRC. No difference was seen in PM and pCRC PATHs in KRAS, BRAF, SMAD2, SMAD4, PTEN. PM had more PATHs in GNAS (8% v. 1%, p < 0.01) while pCRC PATHs were increased in APC (76% v. 48%, p < 0.01), TP53 (72% v. 53%, p < 0.01), ARID1A (29% v. 12%, p < 0.05), PIK3CA (22% v. 15%, p < 0.05) and FBXW7 (13% v. 7%, p < 0.01). LS PM had increased FLCN PATHs (12% v. 2%, p < 0.01); R PM had more PATHs in KMT2D (20% v. 1%, p < 0.01) and RNF43 (13% vs. 3%, p < 0.05). VUS were increased in 39/592 (7%) genes for PM compared to pCRC. No MSI or fusion difference was seen. 53% pCRC (median = 8) pts had TMB ≥8 MMB compared to 43% PMs (median = 7; p = 0.03); no TMB difference was seen for LS, RS or R subgroups. Conclusions: Compared to pCRC, PM had more PATHs in GNAS and less in classic CRC markers APC and TP53. While TMB was generally lower in PM, differences in IHC expression, CNV and VUSs may serve as biomarkers for PM requiring further study.