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.