Background: Previous studies investigating the impact of tumor location on colorectal cancer prognosis only compared two groups by location, e.g., 'right-sided colon vs. left-sided colon,' 'colon vs. rectum,' and 'right-sided (right-sided colon) vs. left-sided (left-sided colon and rectum).' This nationwide multicenter retrospective study aimed to clarify the prognostic impact of tumor location in patients with stage III colorectal cancer by classifying tumors into three groups: right-sided colon, left-sided colon, and rectum.
Methods: Subjects were 9194 patients with stage III colorectal cancer who underwent curative surgery from 1997 to 2012. Relapse-free survival (RFS) after primary surgery and overall survival (OS) after recurrence were examined.
Results: Rectal cancer (n = 2922) was associated with worse RFS compared to right-sided colon cancer (n = 2362) (hazard ratio (HR) 0.65; 95% CI 0.59-0.72; p < 0.001) and left-sided colon cancer (n = 3910) (HR 0.72; 95% CI 0.66-0.78; p < 0.001) after adjusting for key clinical factors (i.e., sex, age, histological type, CEA, adjuvant therapy, T category, and N category). Among patients with recurrence (n = 2823), rectal cancer was associated with better OS compared to right-sided colon cancer (HR 1.23; 95% CI 1.08-1.40; p = 0.002) and worse OS compared to left-sided colon cancer (HR 0.88; 95% CI 0.79-0.99; p = 0.029). Twenty percent of right-sided colon cancer recurrences exhibited peritoneal dissemination, 42% of left-sided colon cancer recurrences were liver metastases, and 33% of rectal cancer recurrences were local recurrences.
Conclusions: The three tumor locations (right-sided colon, left-sided colon, rectum) had different prognostic implications for recurrence after curative resection and overall mortality, suggesting that tumor location serves as a prognostic biomarker in stage III colorectal cancer.
Keywords: Left-sided colon cancer; Rectal cancer; Right-sided colon cancer; Sidedness; Tumor location.