Breast cancer risk of hormone replacement therapy in Japanese women with schizophrenia on antipsychotic treatment: A retrospective cohort study

Abstract

Purpose: This study aimed to identify the risk factors for breast cancer onset in patients with schizophrenia who are receiving antipsychotic treatment. The focus was on understanding how baseline patient characteristics and treatment factors influence breast cancer risk in this population.

Methods: A retrospective cohort study was conducted using a nationwide claims database in Japan, including 12,479 patients with schizophrenia who were receiving antipsychotic medications. The primary outcome was the development of breast cancer. Multivariate Cox regression analysis was employed to identify independent risk factors, with sensitivity analyses conducted using the jackknife and elastic net methods.

Results: Among the 12,479 patients, 22 developed breast cancer during the follow-up period. Baseline age of 38 years or older (hazard ratio (HR) = 4.87, 95 % confidence interval (CI) = 1.41-16.87, p = 0.013) and the use of progestogens (HR = 4.47, 95 % CI = 1.04-19.18, p = 0.044) were identified as independent risk factors for breast cancer onset. Sensitivity analyses confirmed the robustness of these findings, although the study's limited number of events highlighted potential variability in the HRs.

Conclusion: The results suggest that certain treatment factors, particularly the use of progestogens, may increase the risk of breast cancer in patients with schizophrenia who are receiving antipsychotic treatment. Given these findings, careful consideration of treatment plans, including the dosage and duration of hormone replacement therapy and adjustments in antipsychotic treatment, may be warranted. Further research is needed to clarify the interactions between mental disorders, treatment factors, and breast cancer risk.

Keywords: Antipsychotics; Breast cancer; Hormone replacement therapy; Retrospective cohort study; Schizophrenia.