Background: Breast cancer is a major public health concern and the most common cause of cancer-related mortality among women. Compared with the general population, schizophrenia patients have been reported to have lower or similar rates of breast cancer despite several risk factors such as excess smoking, obesity and hyperprolactinemia. However, it has been argued that psychiatric morbidity itself may be the confounding factor that affects cancer incidence and not particularly schizophrenia.
Objective: To evaluate the frequency of breast cancer in a large cohort of female schizophrenia patients utilizing tertiary psychiatric care and to compare it with that of female inpatients with other serious mental illness (SMI).
Method: Data were analyzed from a cohort of 2011 female schizophrenia patients and 6243 female SMI patients. All patient's records in the database were meshed with records of the Israeli National Cancer Registry to identify pathologically confirmed cancer co-morbidity. Cancer incidence rates among patients were compared with the expected incidence in age matched general population for the same time interval.
Results: Among 2011 female schizophrenia patients, 51 (2.5%) developed breast cancer vs. 83 (1.3%) breast cancer cases amongst SMI patients. The standardized incidence ratios (SIR) for breast cancer were low for both patient groups; 0.63 (95% CI, 0.47-0.83) and 0.54 (95% CI, 0.43-0.67) (schizophrenia and SMI respectively).
Conclusions: The findings emphasize that reduced risk of breast cancer is found in a tertiary care cohort of female schizophrenia patients. Yet, breast and ovarian cancer screening for all women who are on long term drugs that induce weight gain or hyperprolactinemia should not be neglected. Our study emphasizes the probable contribution of environmental factors to the mechanisms responsible for this lower risk.