Staging error does not explain the relationship between the number of lymph nodes in a colon cancer specimen and survival

Abstract

Survival in colon cancer is greater in those patients who have more lymph nodes identified at resection and may be due to stage migration, confounding by treatment, social, or clinical characteristics. Identifying factor(s) responsible for the effect may represent an opportunity to improve quality of care for patients with colon cancer by increasing node counts in specimens. Cox proportional hazards models were created to analyze survival of 11,399 patients with stage I-III colon cancer from the Surveillance, Epidemiology and End Results (SEER)-Medicare database. The primary predictor variable was the number of lymph nodes identified. The models allowed adjustment for patient factors, use of chemotherapy, surgical specialty, and the average number of nodes identified by surgeon and hospital pathologist. The number of nodes identified was related to survival. Compared to those with less than 7 nodes, patients with 7 to 11 nodes had a 13% lesser risk of death (hazard ratio [HR], 0.87; 95% confidence interval [CI], 0.76-0.99; P = .037). Patients with more than 12 nodes had a 17% lesser risk (HR, 0.83; 95% CI, 0.73-0.95; P = .005). Adjusting for selected patient demographic characteristics, receipt of chemotherapy, surgical specialty, and the average number of nodes identified per specimen by the surgeon or hospital did not significantly alter the relationship between number of nodes and survival. These findings argue against understaging or confounding as the explanation for the inferior survival observed in patients with fewer nodes identified. National initiatives to increase the number of nodes identified in colon cancer specimens may not improve substantially the cancer-specific outcomes.