Chemotherapy was not independently associated with cancer-specific death in non-metastatic right-sided colon neuroendocrine carcinoma from SEER

The prognostic value of postoperative chemotherapy for non-metastatic right-sided colon neuroendocrine carcinoma (RCNEC) remains unclear. This study aimed to evaluate its association with survival outcomes and to develop a prognostic nomogram for surgically treated RCNEC patients. Surgically treated non-metastatic high-grade RCNEC patients were identified from the Surveillance, Epidemiology, and End Results (SEER) database and were classified into chemotherapy and non-chemotherapy groups according to SEER-recorded chemotherapy status. Propensity score matching (PSM) was performed to balance baseline characteristics between groups. An age-exact matched sensitivity analysis was additionally reported in the supplementary materials. Kaplan–Meier survival analysis and Fine–Gray competing risk models were used to assess the association between chemotherapy and survival outcomes. A prognostic nomogram based on independent predictors was subsequently constructed to estimate individualized CSD probabilities and was evaluated using internal and external validation cohorts. A total of 216 surgically treated non-metastatic RCNEC patients were identified from SEER, including 111 in the non-chemotherapy group and 105 in the chemotherapy group. After 1:1 PSM, neither overall survival nor cancer-specific survival differed significantly between groups ( P = 0.598 and P = 0.422, respectively). In competing-risk analyses, chemotherapy was not associated with a lower cumulative incidence of cancer-specific death (CSD) after matching ( P = 0.219), whereas other-cause death remained significantly lower in the chemotherapy group ( P = 0.002), a finding likely reflecting treatment selection rather than a protective effect of chemotherapy. The age-exact matched sensitivity analysis yielded consistent findings. In multivariable Fine–Gray analysis, chemotherapy was not independently associated with CSD (sHR = 1.21, P = 0.440). The competing risk-based nomogram showed apparent discrimination, with 1-, 3-, and 5-year AUCs of 0.785, 0.819, and 0.755 in the training cohort, 0.895, 0.856, and 0.864 in the internal validation cohort, and 0.795, 0.891, and 0.897 in the external cohort; however, these estimates should be considered preliminary because the training cohort was modest and the external cohort included only 22 patients. In this SEER-based cohort of surgically treated non-metastatic RCNEC, chemotherapy as recorded in SEER was not independently associated with lower CSD in competing-risk analyses; confirmation in clinically annotated datasets is warranted. Given the limitations of registry-coded chemotherapy data, the absence of association should not be interpreted as lack of efficacy of chemotherapy.