The impact of primary tumor sidedness on survival in early-onset colorectal cancer by stage: A National Veterans Affairs retrospective analysis.

Abstract

31 Background: The incidence of early-onset colorectal cancer (EOCRC) is rising. Left-sided colorectal cancer (LCC) is associated with better survival and response to therapy compared to right-sided colon cancer (RCC) in the metastatic setting. Current NCCN guidelines recommend the addition of EGFR inhibitors to KRAS/NRAS wild-type metastatic CRC originating from the left-side only. Whether primary tumor sidedness impacts survival in loco-regional disease and in EOCRC is of clinical interest. Methods: Data from the National VA Cancer Cube Registry was studied. 65,940 cases of CRC were diagnosed between 2001 and 2015. EOCRC (2,096 cases) was defined as CRC diagnosis at age <50 years. ICD codes C18 to C20 were used to delineate patients with RCC vs. LCC. RCC was defined as cancer from the cecum to the hepatic flexure (C18.0-C18.3), LCC from the splenic flexure to the rectum (C18.5-18.CRC; C19 & C20). Transverse cancer (C18.4), overlapping and unidentified sites (C18.8; C18.9) were excluded. Results: EOCRC is more likely to originate from the left-side (66.65% LCC in EOCRC vs. 58.77% in the whole CRC dataset). Overall, LCC has better 5-year OS than RCC in Stage I, III and better 1-year OS in stage IV (Table). Stage II RCC has better 5-year OS than LCC (RC 53.39% vs LC 49.28%). In EOCRC, there is no statistically significant difference between LCC and RCC in Stages I-III. Stage IV EOCRC patients with LCC and RCC have a 1-year OS of 73.23% and 59.84%, respectively. Conclusions: EOCRC is more likely than CRC to originate from the left side. In EORCRC patients, LCC is associated with better OS than RCC only in patients with metastatic disease. In the overall population, LCC is associated with better OS in all states except Stage II. The better prognosis of Stage II RCC might be due to the reported high incidence of MSI-high tumors in this subpopulation. [Table: see text]