Validated Integration of Tumor Deposits in N Staging for Prognostication in Colon Cancer

Importance: Tumor deposits have prognostic value in colon cancer, but the current American Joint Committee on Cancer (AJCC) staging only considers them if there are no concurrent positive lymph nodes. Objective: To devise a staging system for colon cancer by integrating counts of tumor deposits with positive lymph nodes while retaining the current AJCC staging framework. Design, Setting, and Participants: This retrospective cohort study examines data from a large-volume, tertiary care center database (January 2010 through March 2023 with follow-up until December 2023) and the population-based National Cancer Database (January 2010 through December 2020 with follow-up until December 2021). Participants were adults (age 18-75 years) with stage III colon adenocarcinoma who underwent chemotherapy, and had a specified positive lymph node count and tumor deposit count were selected. Exposure: A real positive lymph nodes count was developed and used to derive Sassun-Mayo N/tumor, lymph node, and metastasis (TNM) stages that were compared with the AJCC N/TNM stages. Main Outcomes and Measures: Receiver operating characteristic (ROC) curves and Kaplan-Meier analyses for 3-year overall survival were performed to assess the efficiency of the 2 staging systems. The concordance index was used for validation using the National Cancer Database. Results: From a total patient number of 11 162 (institutional) and 848 704 (national), the final patient numbers were 788 and 77 790, respectively. The institutional database patients had a mean (SD) age of 58.5 (11.5) years; there were 433 male patients (54.9%) and 355 female (45.1%). The national database patients had a mean (SD) age of 59.3 (10.6) years; there were 40 315 male patients (51.8%) and 37 475 female (48.2%). ROC curve areas were improved using the Sassun-Mayo stages (3-year death for AJCC TMN, 0.63 [95% CI, 0.57-0.69] vs 0.66 [95% CI, for 0.60-0.72] for Sassun-Mayo TNM). Kaplan-Meier curves revealed visible overlaps among AJCC N stages, which were absent in the Sassun-Mayo N stages. The concordance index in the Sassun-Mayo N/TNM stages was 0.611 and 0.616, respectively, while in the AJCC N/TNM stages, it was 0.598 and 0.606, respectively. Patients upstaged from N1 to N2 (n = 10 307; 13.2%) had a 3-year overall survival rate nearly identical to that of AJCC N2a patients. Additionally, 3001 patients (3.9%) were upstaged from N2a to N2b, indicating that 13 308 patients (17.1%) with stage III colon cancer across cohorts were understaged. Conclusions and Relevance: This study found that Sassun-Mayo N/TNM staging provided superior overall survival stratification compared with the current AJCC staging, suggesting that their implementation could improve prognostication in colon cancer.