Association of Schizophrenia With the Risk of Breast Cancer Incidence: A Meta-analysis.

Importance: Patients with schizophrenia are considered to have many risk factors for the development of cancer. However, the incidence of breast cancer in women with schizophrenia compared with the general population remains uncertain.

Objective: To perform an updated meta-analysis to evaluate the association between schizophrenia and the risk of breast cancer.

Data Sources: A systematic search of the PubMed and EMBASE databases was conducted using the search terms schizophrenia, schizophrenic, psychosis, combined with breast and cancer, tumor, neoplasm, or carcinoma. The final literature search was performed on August 15, 2017.

Study Selection: Cohort studies reporting the standardized incidence ratio (SIR) for the risk of breast cancer in women with schizophrenia compared with the general population.

Data Extraction and Synthesis: The meta-analysis adhered to Meta-analysis of Observational Studies in Epidemiology and the Cochrane Handbook for Systematic Reviews of Interventions. Data extraction was performed independently. A random-effects model was used to pool the results, and a recently proposed prediction interval was calculated to describe the heterogeneity.

Main Outcomes and Measures: The SIR for the risk of breast cancer in women with schizophrenia compared with the general population or those without schizophrenia.

Results: Twelve cohorts including 125 760 women were included in this meta-analysis. The results of the meta-analysis showed that schizophrenia was associated with a significantly increased risk of breast cancer incidence in women (SIR, 1.31; 95% CI, 1.14-1.50; P < .001), with significant heterogeneity (P < .001; I2 = 89%). Substantial between-study variance was also suggested by the wide prediction interval (0.81-2.10), which indicated that it is possible that a future study will show a decreased breast cancer risk in women with schizophrenia compared with the general population. The subgroup analysis results showed that the association was not significantly affected by whether breast cancer cases were excluded at baseline or the sample size of the included studies.

Conclusions and Relevance: The incidence of breast cancer in women with schizophrenia is higher than that of the general female population. However, significant heterogeneity exists among the included studies. Women with schizophrenia deserve intensive prevention and treatment of breast cancer.