Underutilization or appropriate care? Assessing adjuvant chemotherapy use and survival in 3 heterogenous subpopulations with stage II/III colorectal cancer within a large integrated health system

Clinical guidelines have recommended adjuvant chemotherapy (ACT) for patients with high-risk stage II colon cancer, although the survival benefit is unclear. ACT is also recommended for patients with stage III colon cancer to reduce the risk of recurrence and mortality. For stage II/III rectal cancer, however, the role of perioperative chemotherapy (PCT, adjuvant or neoadjuvant) remains controversial, resulting in substantial variation in its use in clinical practice. To understand real-world use and predictors of ACT or PCT use and survival outcomes in 3 heterogeneous patient groups with colorectal cancer (CRC), and to inform the evidence gap between guideline-based care and clinical practice. This retrospective cohort study included patients with an initial stage II/III CRC diagnosis between 2008 and 2013 identified from Kaiser Permanente Southern California electronic health record databases. Patients were eligible if they were aged 18-74 years at diagnosis and received primary curative surgery. We fitted mixed effects logistic regression models to evaluate predictors of ACT receipt and Cox proportional hazards models on propensity score-matched (PS-matched) samples to assess the association between ACT/PCT receipt and survival. We included 1,690 patients with colon cancer (stage II: 820 and stage III: 870) and 587 patients with rectal cancer (stage II: 241 and stage III: 346). We found that 65% of patients with high-risk stage II colon cancer, 15% of those with stage III colon, and 15% of those with stage II/III rectal cancer did not receive ACT/PCT. Patients with stage II colon cancer with T4 stage (odds ratio [OR] = 5.79, 95% CI = 3.33 - 10.06) and a lower comorbidity score were more likely to receive ACT (high vs low Charlson score: OR = 0.69, 95% CI = 0.55 - 0.87). Patients with stage III rectal cancer were more likely to receive PCT than those with stage II disease (OR = 7.85, 95% CI = 2.07 - 29.74). Patients with another cancer diagnosis prior to CRC diagnosis were less likely to receive PCT (OR = 0.37, 95% CI = 0.16 - 0.85). ACT/PCT use was associated with improved overall survival among patients with high-risk stage II colon cancer (PS-matched hazard ratio [HR] = 0.42, 95% CI = 0.25 - 0.70) and those with stage III CRC (stage III colon: PS-matched HR = 0.3, 95% CI = 0.25 - 0.36; stage III rectal: PS-matched HR = 0.2, 95% CI = 0.13 - 0.31). We found potential underuse of appropriate chemotherapy treatment in patients with high-risk stage II colo