Impact of Schizophrenia Spectrum Disorders on the Receipt of Invasive and Systemic Therapy for Colorectal Cancer: A Nationwide Multicenter Retrospective Cohort Study in Japan

Introduction: This study examined treatment disparities for colorectal cancer among patients diagnosed with schizophrenia spectrum disorders (SSD), focusing on invasive treatments and stage-appropriate systemic therapy within a universal healthcare system.
Method: In this nationwide retrospective cohort study (2018–2021), we identified 248,966 colorectal cancer patients, including 2337 diagnosed with SSD, using linked cancer registry and insurance claims data in Japan. The presence of SSD was classified according to ICD-10 codes F20–29. We used multivariable logistic regression to compare the odds of receiving stage-appropriate adjuvant chemotherapy and systemic therapy, as well as the odds of receiving surgical or endoscopic treatments, between the two groups. The analysis adjusted for age, sex, clinical stage, and scores on the Charlson Comorbidity Index and Barthel Index.
Results: The clinical stage distribution at diagnosis for colorectal cancer differed significantly between patients with SSD and those without psychiatric disorders (p < 0.001). After adjusting for clinical stage and other covariates, patients with SSD demonstrated significantly lower odds of receiving surgical or endoscopic treatment (adjusted odds ratio [aOR], 0.83; 95% CI, 0.73–0.94). The disparities were more pronounced for systemic therapy; patients with SSD had substantially lower odds of receiving adjuvant chemotherapy for stage III disease (aOR, 0.33; 95% CI, 0.26–0.41) and systemic therapy for stage IV disease (aOR, 0.23; 95% CI, 0.17–0.31).
Conclusion: Patients with SSD encounter substantial disparities in accessing standard colorectal cancer care, particularly systemic therapies. These findings highlight the urgent need for interventions to ensure equitable cancer treatment for this vulnerable population.