Examining stage IIB survival in a population-based cohort of patients with colorectal cancer

BACKGROUND: In Nova Scotia, Canada, a previous study of colorectal cancer (CRC) cases diagnosed between January 1, 2001, and December 31, 2005, found that patients with stage IIB CRC had similar 5-year overall survival (OS) to those with stage IIIC cancer. This study sought to examine factors contributing to the observed stage IIB outcome, specifically nodal harvest, receipt of chemotherapy, and use of a new coding system to derive stage. METHODS: The provincial cancer registry identified all CRC cases diagnosed during the study period and staged this cohort using the Collaborative Stage (CS) Data Collection System. All patients with stage II and III cancer in the cohort were examined. Kaplan-Meier (KM) survival curves compared 5-year OS for patients with stage IIB cancer based on the factors of interest, and compared patients with stage IIB cancer to those with stage IIA and III cancer. RESULTS: OS for patients with stage IIB cancer (n = 187) was 44.7%, and differed depending on adequacy of nodal harvest (P =.005) and whether pathological or clinical/mixed evidence was used to derive stage (P =.013). Pathologically-staged patients with stage IIB cancer who had adequate nodal harvest had marginally improved OS compared to pathologically-staged patients who had inadequate nodal harvest (P =.07), and improved survival compared to patients with clinical/mixed stage (P =.004). Pathologically-staged patients with stage IIB cancer with adequate nodal harvest demonstrated similar 5-year OS to those with stage IIA and III cancer (P =.52 and P =.25, respectively). Cox proportional hazards models supported these findings. CONCLUSIONS: The inclusion of clinical/mixed evidence into staging classification and, perhaps to a lesser extent, the adequacy of nodal harvest appear to contribute to the observed worse survival for patients with stage IIB versus stage III cancer.