Impact of pre-existing schizophrenia spectrum disorder on the receipt of invasive and systemic therapy for gastric cancer: a multicenter nationwide cohort study in Japan

Abstract Background Patients with schizophrenia spectrum disorders (SSD) experience higher cancer mortality, partly because of later-stage diagnosis and lower rates of recommended treatments. While treatment disparities have been reported across several cancer types, no study has specifically examined stage-appropriate treatment for gastric cancer among patients with SSD. Methods We conducted a retrospective cohort study using a nationwide Hospital-Based Cancer Registry linked to administrative data in Japan. Patients who received initial treatment for gastric cancer between 2018 and 2021 were included. Multivariable logistic regression models examined the association between SSD and the receipt of stage-appropriate cancer treatments, adjusting for age, sex, clinical stage, Charlson Comorbidity Index, and Barthel Index. Results Among 189 447 patients from 709 hospitals, 1312 had SSD. Patients with SSD were more likely to be diagnosed at advanced stages. In crude analysis, SSD was associated with lower rates of surgical or endoscopic treatment; however, this association was not statistically significant after adjustment (adjusted odds ratio [aOR], 0.90; 95% confidence interval [CI], 0.75–1.08). In contrast, SSD was independently associated with lower rates of postoperative adjuvant chemotherapy for pathological stage II/III disease (aOR, 0.64; 95% CI, 0.45–0.91) and systemic therapy for stage IV disease (aOR, 0.36; 95% CI, 0.28–0.47). Conclusions Among patients with gastric cancer, SSD was associated with reduced receipt of systemic therapy but not surgical or endoscopic treatment. Efforts to improve early detection among patients with SSD may be important for reducing treatment disparities, alongside strengthened support for systemic therapy to ensure equitable access to guideline-recommended gastric cancer care.