Investigating the Relationship between Schizophrenia with Risk of Breast Cancer Incidence: A Systematic Review and Meta-Analysis of Cohort Studies

Objective: Schizophrenia seems to have a complex association with various types of cancer, exerting a protective effect against some cancers while being a risk factor against some others. Therefore, we intended to conduct an updated systematic review and meta-analysis in order to examine the relationship between schizophrenia and the risk of breast cancer incidence. Method: We did a systematic search of databases, namely Web of Science, Scopus, Embase, PubMed, and PsycINFO up to August 15, 2024. Screening and data extraction were performed independently. Data was analyzed using Stata16 software. We used the random effect model to pool the results, while the heterogeneity between studies was calculated using Cochran's Q test and (I2) index. Results: We found 15 studies, among which 12 were included in this meta-analysis. The results indicated that the risk of breast cancer development is significantly increased in women with schizophrenia (SIR: 1.43, 95% CI: 1.08-1.85, P < 0.01; IRR: 1.19, 95% CI: 1.13-1.26, P < 0.01). Subgroup analysis revealed significant differences in the incidence of breast cancer rates among women with schizophrenia based on geographic location and duration of follow-up. Conclusion: The results indicate that schizophrenia increases the risk of developing breast cancer. Therefore, taking preventive measures concerning breast cancer among women with schizophrenia is crucial. Additionally, regular screening programs should be implemented to ensure early diagnosis and treatment in case breast cancer is detected.