Evaluating the survival benefit of adjuvant chemotherapy based on tumor deposit status in stage II colon cancer patients from SEER database

Colon cancer is a common malignancy with a high mortality rate. The staging of tumor deposits (TD) in colon cancer prognosis has been a subject of controversy. The aim of this study was to evaluate the impact of adjuvant chemotherapy (ACT) on overall survival (OS) and cancer-specific survival (CSS) in stage II colon cancer patients, with a specific focus on whether TD status modifies the treatment effect and to validate the AJCC 8th edition criteria for TD staging. We identified eligible patients with stage II colon cancer (N = 21,499) from the SEER database, covering the period from January 2000 to December 2018. We used subgroup analysis to explore the relationship between chemotherapy and tumor deposits, and a forest plot was drawn. A 1:1 Propensity Score Matching (PSM) was utilized to create a matched cohort with balanced baseline characteristics, reducing bias. After PSM, ACT demonstrated significant OS benefits in both the overall population (HR, 0.87; P = 0.01) and the TD-free subgroup (HR, 0.88; P = 0.018), while the negative association with CSS was no longer significant (HR, 1.13; P = 0.079), indicating effective bias control. Interaction analyses confirmed statistically comparable treatment effects of ACT irrespective of TD status for both OS and CSS. Multivariate analysis identified ACT as an independent prognostic factor for improved OS, while tumor deposits were a significant independent adverse prognostic factor for both CSS and OS (all P < 0.001). This study confirms that tumor deposits is an independent and significant prognostic factor for colorectal cancer patients and provides some evidence for the accuracy of the AJCC 8th edition in classifying the presence of tumor deposits as N1c.