Risk factors for relapse based on the molecular profiling of Japanese patients with stage II colorectal cancer.

215 Background: The association between the molecular profiles and prognosis of Stage II colorectal cancer (CRC) remains unclear. This study aimed to evaluate the long-term outcomes of Stage II CRC based on the molecular profiling and to examine the risk factors for relapse. Methods: We retrospectively enrolled Japanese patients with pStage II CRC without pre- and/or postoperative adjuvant therapy and whose surgically resected specimens were evaluated using gene expression and whole exome analyses from January 2014 to December 2018. We evaluated the 5-year overall survival (OS) and relapse-free survival (RFS), and examined the risk factors for RFS. Results: We evaluated 322 patients with pStage II CRC, including 126 (39.1%) with right colon cancer, 133 (41.3%) with left colon cancer and 63 (19.6%) with rectal cancer. There were 87 patients (27.0%) with pT4, 175 (54.3%) with venous invasion, 120 (37.3%) with lymphatic invasion, and 68 (21.1%) with perineural invasion. Whole exome analyses revealed that there were 48 patients (14.9%) with MSI-High, and the presence of mutations in key genes for colorectal cancer development was as follows: APC , 245 (76.1%); TP53 , 208 (64.6%); KRAS , 134 (6.5%); PIK3CA , 64 (19.9%); FBXW7 , 27 (8.4%); and BRAF , 21 (6.5%). The 5-year OS and RFS rates were 98.0% and 90.7%, respectively. According to the consensus molecular subtype (CMS) classification based on gene expression, 76 patients (23.6%) had CMS4 and a significantly lower RFS than the other patients (5-year RFS: 83.8% vs. 92.9%, p=0.017). The independent risk factors for RFS were perineural invasion (Hazard ratio [HR] 5.316, p<0.001) and CMS4 (HR 2.399, p=0.020). Conclusions: Molecular profiling of Stage II CRC to assess the risk factors for relapse may contribute to the indication and drug selection for postoperative adjuvant chemotherapy and lead to personalized treatment to improve prognosis.