A comparative study of the adjuvant management of and survival from colon cancer in the two Canadian provinces of Newfoundland & Labrador and Ontario

INTRODUCTION: The crCIHRt collaboration between Newfoundland and Ontario (2000-present) is an interdisciplinary study of the determinants of and impact from colorectal cancer (CRC) between these two Canadian provinces. It includes an evaluation of the adjuvant treatment of CRC and overall survival from this common disease. Clinical Practice Guidelines (CPGs) for the adjuvant treatment of surgically curable (Stage I-III) colon cancer have not previously been evaluated in Canada. Canadian Cancer Statistics (CCS) have shown that overall survival from CRC is better in Ontario. The aims of this study were to evaluate whether adjuvant chemotherapy for Stage I-III colon cancer in the two provinces is concordant with accepted CPGs and to contrast overall survival from colon cancer in comparison with data from CCS. -- METHODS: In Newfoundland, all incident cases of colon cancer diagnosed between January 1, 1999 and December 31, 2000, ages 20-74 were included. In Ontario, all patients with a high- or intermediate-risk pedigree and a random sample of those with a low-risk pedigree for colon cancer, ages 18-74, diagnosed between January 1, 1999 and June 30, 2000 were offered participation in the study. Data was retrospectively retrieved using a standardized extraction form and quality assurance was undertaken through a random re-extraction by two physician researchers. The charts of all patients with stage II disease were qualitatively assessed to determine what factors were used to recommend chemotherapy to these patients. This was contrasted with CPGs recommending chemotherapy only in stage II patients with 'high-risk' features. An overall survival comparison between the two provinces was contrasted with age-standardized projections from CCS suggesting that Newfoundland experiences a worse overall survival than Ontario from CRC. -- RESULTS: 173/274 (63%) and 364/514 (71%) eligible patients consented in Newfoundland and Ontario, respectively. -- No one with stage I colon cancer in either province received adjuvant chemotherapy. 20/55 patients (36%) in Newfoundland and 44/116 evaluable patients (38%) in Ontario received adjuvant therapy for stage II disease. 18/41 patients (44%) in Newfoundland and 30/53 patients (57%) in Ontario with high-risk features received adjuvant treatment, significantly higher than patients without high-risk features. On multivariate analysis, age < 50 years was shown to be an independent predictor for the use of chemotherapy in stage II patients. 45/52 patients (87%) in Newfoundland and 108/115 patients (94%) in Ontario with stage III disease received adjuvant chemotherapy. -- Kaplan-Meier survival analysis revealed that overall 5-year survival from colon cancer was significantly better in Ontario. Exclusion of patients consented by proxy in Newfoundland negated this survival advantage. -- DISCUSSION: Concordance with CPGs for adjuvant chemotherapy in stage II colon cancer was not optimal. This may reflect selection bias of referring surgeons, a paucity of level I evidence and the belief that other factors such as age may play a role in predicting outcome. Ontario showed a significantly better overall survival, however, this advantage was lost when bias introduced through recruitment methods was controlled for. Methods to ensure consistency and appropriate resource allocation in the development, adaptation and implementation of CPGs and the importance of minimizing bias in survival analysis are discussed