Sidedness matters: Surrogate biomarkers prognosticate colorectal cancer upon anatomic location.

Abstract

523 Background: Recent evidence indicate that the anatomic location of primary tumors across the colon correlate with survival in the metastatic setting, whereas left-sided tumors may exhibit superior survival compared with right-sided. The Oncotype DX, a 12-gene colon cancer assay, is a clinically validated predictor of recurrence risk in stage II colorectal cancer (CRC) patients. Previous studies had indicated that CDX2-negative colorectal tumors are often associated with several adverse prognostic variables. Recently, it has been shown that without adjuvant chemotherapy, CDX2-negative stage II CRC tumors were associated with a lower rate of disease-free survival than CDX2-positive stage II CRC tumors. We aimed to evaluate whether these validated two prognostic biomarkers may correlate with primary tumor location, and whether tumor location may reflect differential prognosis in stage II CRC. Methods: We retrospectively analyzed a cohort of patients with T3 mismatch repair proficient (MMR-P) stage II CRC for whom 12-gene assay was performed (between 1/2011-2/2016). Pathological report was reviewed for exact primary tumor location and CDX2 immunostaining. Recurrence score (RS) and CDX2 expression were correlated with primary tumor location. Results: The analysis included 1087 patients with MMR-P stage II CRC (median age 69 years (range 29-93)). Tumor distribution across the colon was as follows: 46% (n = 500) were right-sided (cecum, ascending colon, transverse colon) and 54% (n = 587) were left-sided (splenic flexure, descending colon, sigmoid colon and rectum). Recurrence score was higher in right-sided tumors compared with left-sided tumors (p = 0.01). The RS gradually decreased across the colon (cecum - highest score, sigmoid-lowest score, p = 0.04). Right-sided tumors exhibited more CDX2-negative tumors compared with left-sided tumors (p = 0.07). Conclusions: Our study indicate that right-sided colorectal tumors may display worse prognosis compared with left-sided tumors in MMR-P stage II CRC. Primary tumor location may serve as a prognostic factor that should be accounted for recurrence risk assessment and consideration of adjuvant treatment.