Differences of RAS/BRAF mutations between ISCC and RSCC in a Chinese population.

Abstract

e15636 Background: According to the location and different clinical manifestations, colon cancer can be divided into left-sided colon cancer (LSCC) and right-sided colon cancer (RSCC). There are significant differences in morphology, molecular biology, and drug sensitivity between these two type. In addition, colorectal cancer is associated with the mutation of many essential tumor suppressor genes, such as proto-oncogene (KRAS), serine/threonine protein kinase (BRAF), etc. At that point, this study retrospectively analyzed the RAS/BRAF mutation landscape and studied the gene expression differences between RAS/BRAF-mutant and wild-type patients respectively in LSCC and RSCC, to provide some reference for potential treatment plans. Methods: We retrospectively profiled the somatic mutations of 497 patients with colon cancer from the General Hospital of Southern Theatre Command and the TCGA database using 808-gene-panel target-capture next-generation sequencing. Tumor mutation burdens (TMB) were calculated using an Acornmed panel with 808 cancer-related genes. Results: Among 415 LSCC, 48.7% (n = 202) patients harbored RAS mutations, of which 183 carried KRAS mutations and 19 had NRAS mutations. Five main subtypes of KRAS mutation were detected including G12D (28.7%), G12V (17.5%), G13D (13.2%), A146T(8.5%), G12C (7.9%). 3% (11) of LSCC patients were found to have BRAF mutation, including BRAF V600E(63.6%), D594G(18.2%), G466E(9.1%), K601E(9.1%). We explored differentially expressed genes between RAS/BRAF-mutant and wild-type patients. The top5 mutant genes found only in LSCC RAS/BRAF-mutant cohort include JAK2(3%), TERT(2%), MSH6(2%), KMT2A(1%), NOTCH1(1%). In contrast, genes found only in LSCC patients with RAS/BRAF wild type include LATS2(2%), SMARCA4(2%), CBL(1%), SLX4(1%), CDKN2A(1%). Among 82 RSCC, 50% (41) patients harbored RAS mutations, of which 39 carried KRAS mutations and 2 carried NRAS mutations. 9% (39) of RSCC patients were found BRAF mutation, and the BRAF V600E was the only subtype found in the RSCC. In terms of differentially expressed genes, the top5 mutant genes found only in RAS/BRAF-mutant RSCC include NSD1(6%), ASXL2(4%), BARD1(4%), PPP2R1A(4%), SPRED1(4%), while genes found only in RAS/BRAF wild-type RSCC include ERBB2(17.6%), DICER1(11.8%), EP300(11.8%), ARID2(9%), BRIP1(9%).The TMB of RAS/BRAF wild-type RSCC patients was 33.2 mut/Mb, significantly higher than that of RAS/BRAF wild-type LSCC patients (7.0 mut/Mb, P = 0.01). Conclusions: RAS mutation and subtype were almost the same in LSCC and RSCC cohorts. BRAF mutation mainly occurred in RSCC, and the mutation subtype in RSCC was found only V600E, but we found three other BRAF subtypes D594G, G466E, and K601E in the LSCC cohort. Considering the differential expression genes in RAS/BRAF-mutant and wild-type cohorts in RSCC and LSCC patients, there may be more options for genetic targets in the future for LSCC and RSCC treatment.