Improving Prognostic Accuracy in Locally Advanced Rectal Cancer: Integrating Tumor Deposits with Lymph Node Metastases—A Retrospective Study

Objectives: This study aimed to investigate the impact of TDs on the survival of patients with locally advanced rectal cancer (LARC). Additionally, we propose a novel staging method that combines TDs and lymph node metastases (LNMs) to enhance prognostic accuracy. Methods: Patients with LARC were retrospectively identified from the Surveillance, Epidemiology, and End Results (SEER) database and a Sun Yat-sen University (SYSU) cohort. Propensity score matching (PSM) was utilized to minimize selection bias when evaluating TDs. We quantitatively stratified TDs counts and integrated them with regional LNMs to formulate a novel tumor node metastasis (TNM) staging system. Furthermore, a prognostic nomogram incorporating TDs was constructed and validated to predict survival. Results: Overall, 19,991 patients were included in the SEER database, with 2667 (13.3%) TDs-positive and 17,324 (86.7%) TDs-negative tumors. After PSM, multivariate Cox analysis reveals that TDs are an independent adverse prognostic factor (HR = 1.521, 95% CI: 1.366–1.693, p < 0.001). Patients with high-risk group (TDs > 4) at any TNM stage exhibit OS comparable to or worse than that of stage IIIC disease. For patients staged as T4N2M0, the high-risk group (TDs > 4) demonstrates OS equivalent to stage IV disease. The nomogram achieved C-indices of 0.713 (training cohort, n = 8586) and 0.789 (external validation cohort, n = 304), with AUCs of 0.774 (3-year) and 0.710 (5-year). Conclusions: The presence of TDs is associated with poorer OS, and integrating TDs with LNMs improves the accuracy of TNM staging. The nomogram (C-index = 0.789) provides enhanced prognostic stratification and survival prediction.