Distinct expression and prognostic value of CA19-9 between right- and left-sided colorectal cancer.

PURPOSE: Right- and left-sided colorectal cancers (CRCs) exhibit distinct clinicopathological and molecular characteristics; however, the differences in tumor marker expression between the two sides remain unclear. We investigated whether tumor marker levels and their clinical relevance vary by tumor-sidedness, which has distinct embryological origins. METHODS: We analyzed 800 patients with colorectal adenocarcinoma (293 right-sided and 507 left-sided) who underwent surgery at Saga University Hospital between January 2012 and December 2024. Serum carcinoembryonic antigen and carbohydrate antigen 19 - 9 (CA19-9) levels were compared between the groups, and their associations with early recurrence were evaluated. RESULTS: Right-sided CRCs was more frequent in older patients, women, and those with mucinous histology. After adjusting for baseline characteristics, serum log CA19-9 levels remained significantly higher in right-sided CRC (1.22 ± 0.59 vs. 1.14 ± 0.45, P = 0.034). Among the 617 patients who underwent curative resection, 53 (8.6%) experienced early recurrence. A multivariable analysis identified log CA19-9 and the pathological stage as independent predictors of early recurrence, with the association for CA19-9 remaining significant only in right-sided disease (odds ratio, 3.710; 95% confidence interval, 1.509-9.726; P = 0.004). CONCLUSION: The serum CA19-9 levels were higher in right-sided CRC after adjusting for baseline characteristics and predicted early recurrence only in right-sided disease.