Real-world patterns of chemotherapy administration and attrition among patients with metastatic colorectal cancer.

OBJECTIVE To assess the real-world patterns of systemic treatment attrition rates among patients with metastatic colorectal cancer. METHODS Databases based from the provincial cancer registry and electronic medical records in Alberta were accessed, and cases with a de novo diagnosis of metastatic colorectal cancer with no history of other primary cancers (2004-2017) were reviewed. Rates of chemotherapy administration in first and subsequent lines of treatment were assessed. Multivariable logistic regression analysis for factors associated with non-administration of chemotherapy was evaluated. The impact of administration of all three chemotherapy agents (fluoropyrimidines, oxaliplatin, and irinotecan) across the course of treatment was assessed through multivariable Cox regression analysis with time-dependent covariates. RESULTS A total of 4179 patients with metastatic colorectal cancer were included in the current study. This includes 1988 patients receiving at least one cycle of chemotherapy and 2191 patients who did not receive any chemotherapy. The following factors were associated with a higher probability of no chemotherapy use: older age (OR 1.064; 95% CI 1.057-1.070), higher Charlson comorbidity index (OR 1.444; 95% CI 1.342-1.554), female sex (OR for male sex versus female sex 0.763; 95% CI 0.660-0.881), rural residence (OR for residence in zone 2 (Calgary) versus zone 5 (North zone) 0.346; 95% CI 0.272-0.440), proximal tumor location (OR 1.255; 95% CI 1.083-1.454), and earlier year at diagnosis (OR (continuous) 0.895; 95% CI 0.879-0.911). Within the cohort of patients who received at least one cycle of chemotherapy, 42.5% received one line of chemotherapy only, and 30.5% received two lines of chemotherapy. The use of all three chemotherapy drugs was associated with better overall survival (HR 3.305; 95% CI 2.755-3.965) and colorectal cancer-specific survival (HR 3.367; 95% CI 2.753-4.117). CONCLUSIONS A considerable proportion of metastatic colorectal cancer patients who received active chemotherapy in this population-based study received only one line of therapy. This highlights the significance of choosing effective treatments in the first-line treatment as the attrition rate is high. Furthermore, the use of all three chemotherapy agents across the course of treatment was associated with better outcomes.