Clinical significance of metastatic tumor deposit foci in rectal cancer in the lateral pelvic lymph node area

Background Although previous studies have demonstrated that tumor deposits (TDs) are associated with worse prognosis in colon cancer, their clinical significance in rectal cancer has not been fully elucidated, especially in the lateral pelvic lymph node (LPLN) area. This study aimed to clarify the clinical significance of TDs, focusing on the number of metastatic foci, including lymph node metastasis (LNM) and TD, in the LPLN area. Methods This retrospective study involved 226 consecutive patients with cStage II/III low rectal cancer who underwent LPLN dissection. Metastatic foci, including LNM and TD, in the LPLN area were defined as lateral pelvic metastasis (LP-M). LP-M was evaluated according to LP-M status: presence (absence vs presence), histopathological classification (LNM vs TD), and number (1 to 3 vs 4 or more). We evaluated the relapse-free survival of each model and compared them using the Akaike information criterion (AIC) and Harrell’s concordance index (c-index). Results Forty-nine of 226 patients (22%) had LP-M, and 15 patients (7%) had TDs. The median number of LP-M per patient was one (range, 1-9). The best risk stratification power was observed for number (AIC, 758; c-index, 0.668) compared with presence (AIC, 759; c-index, 0.665) or histopathological classification (AIC, 761; c-index, 0.664). The number of LP-M was an independent prognostic factor for both relapse-free and overall survival, and was significantly associated with cumulative local recurrence. Conclusion The number of metastatic foci, including LNM and TD, in the LPLN area is useful for risk stratification of patients with low rectal cancer.