Breast cancer may be more prevalent in women with schizophrenia than in the general female population, according to a recent meta-analysis published in JAMA Psychiatry.
Following guidelines established by the Cochrane Handbook for Systematic Reviews of Interventions and the Meta-analysis of Observational Studies in Epidemiology, investigators set out to analyze cohort studies from the EMBASE and PubMed databases to determine the relative breast cancer risk in women with schizophrenia. The databases were searched using the terms schizophrenic, schizophrenia, and psychosis in combination with breast and cancer, carcinoma, tumor, or neoplasm. Of the 832 cohort records found through this search, 12 cohorts were deemed suitable for inclusion in the meta-analysis, with 125,760 total women involved in the studies.
Subgroup analysis showed a significant association between schizophrenia and a greater prevalence of breast cancer when the cohorts included more than 100 cases of breast cancer or excluded any incidence of cancer that occurred before schizophrenia was diagnosed. In the studies that included fewer than 100 cases of breast cancer and did not specifically state that any cases of breast cancer occurred before the schizophrenia diagnosis were excluded from the study, the association was not significant.
Limitations of the meta-analysis include residual factors such as diet and the use of antipsychotics, which can increase prolactin levels. Any heterogeneity in the meta-analysis could not be analyzed in full because individual patient data were not available to study investigators. It is possible that factors such as patient age at onset of breast cancer, cancer subtypes, or treatment could significantly alter the association found in the meta-analysis.
Previous findings show that schizophrenia seems to be associated with a lower risk for certain kinds of cancer, leading researchers to theorize that genetic factors leading to schizophrenia may also protect against cancer. However, patients with schizophrenia often exhibit lifestyle habits that could increase cancer risk, and a recent study has demonstrated a higher cancer mortality rate in these patients that does not necessarily correspond to cancer risk.
Although this meta-analysis did indicate that higher rates of breast cancer can be found among women with schizophrenia, the substantial variance between studies leads investigators to state that a future analysis may find opposing results. “Future studies are needed to determine the association between schizophrenia and the different pathologic subtypes of breast cancer as well as whether the association may be affected by the woman’s age at breast cancer onset, antipsychotic medications used, and the cancer subtype.”
Zhuo C, Triplett PT. Association of schizophrenia with the risk of breast cancer incidence: a meta-analysis [published online March 7, 2018]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2017.4748