Patients with schizophrenia are considered to have many risk factors for the development of cancer. But the incidence of breast cancer in women with schizophrenia compared with the general population remains uncertain. A new study, published in JAMA Psychiatry, evaluate the link between schizophrenia and the risk of breast cancer, and found that incidence of breast cancer is higher among women with schizophrenia than the incidence among the general female population.
“Because schizophrenia has been associated with lowered risks of many types of cancer, including colorectal cancer, malignant melanoma and prostate cancer, it has been hypothesized that the genetic factors involved in the pathogenesis of schizophrenia may be protective against cancer,” The study authors wrote.
In this meta-analysis, researchers conducted a systematic search of clinical databases to examine the association between schizophrenia and the risk of breast cancer. They included cohort studies that reported the standardized incidence ratio (SIR) of the risk for breast cancer in women with schizophrenia compared with the general population. To pool the results, they used a random-effects model then calculated a prediction interval to determine heterogeneity.
The meta-analysis included 12 cohorts comprising 125,760 women. Schizophrenia was associated with a significantly higher risk for breast cancer incidence in women (SIR = 1.31), with significant heterogeneity. There was substantial between-study variance, which was reflected by the wide prediction interval (0.81-2.1), suggesting that future research may show a smaller risk for breast cancer among women with schizophrenia compared with the general female population.
Sensitivity analysis that omitted one study at a time revealed no significant changes in the results; SIRs varied between 1.29 to 1.38. Subgroup analysis revealed that the association between schizophrenia and higher incidence of breast cancer was not significantly affected by whether breast cancer cases were excluded before schizophrenia diagnosis, or by the sample size of the included cohort studies.
“Our findings highlight that intensive prevention and treatment against breast cancer are warranted for women with schizophrenia,” Zhuo and Triplett wrote. “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.”