Prognostic significance and clinicopathologic prediction of tumor deposits in non-metastatic colon mucinous adenocarcinoma

Colon mucinous adenocarcinoma (CMAC) is a prognostically unfavorable subtype in which tumor deposits (TDs) are an under-recognized adverse feature with uncertain prognostic relevance and a risk of under-detection. From the SEER database we assembled 1372 non‑metastatic CMAC patients (7:3 training/internal‑validation split) plus an external cohort of 398 patients from the Affiliated Hospital of Qingdao University, using Kaplan–Meier analysis, multivariable Cox regression, and logistic regression to characterize TD prognosis and to develop a model predicting TD presence. TDs were independently associated with poorer cancer-specific survival after adjustment for positive lymph node (PN) burden; no statistically significant TD × PN interaction was detected ( P > 0.05), although the PN = 0 subgroup estimate was imprecise and not statistically significant. A nomogram using six routine clinicopathologic predictors—tumor size, site, grade, invasion depth, PN count, and perineural invasion—predicted TD presence with good discrimination (AUC = 0.820, 0.768, 0.784 for training, internal‑validation, and external cohorts), good calibration (Brier 0.095, 0.098, 0.086), and positive net benefit at 5–25% threshold probabilities. Collectively, TDs provide adverse prognostic information after accounting for nodal burden in CMAC, and the nomogram, externally validated only for TD prediction, estimates the probability of recorded TD positivity and may help identify cases warranting additional pathological attention; the survival findings require further validation in multicenter studies.