Women with schizophrenia are at increased risk of breast cancer

Commentary on: Chou AIW, Wang Y-C, Lin C-L, et al. Female schizophrenia patients and risk of breast cancer: a population-based cohort study. Schizophrenia Research 2017;188:165–171.

What is already known on this topic

Research into rates of breast cancer in women with schizophrenia shows conflicting results, with reports of increased, decreased and the same risk as the general population. This is despite women with schizophrenia possibly being at increased risk of breast cancer through use of antipsychotic medications, many of which increase prolactin, a hormone involved in cellular differentiation of the mammary glands. This study¹ investigated rates of breast cancer in individuals with schizophrenia compared with the general population.

Methods of the study

The authors used large databases of routinely collected health data to compare rates of breast cancer in women with schizophrenia receiving antipsychotics (n=10 727) with rates in women without schizophrenia nor receiving antipsychotic drugs (n=10 727). The groups were matched on the following variables known to be associated with breast cancer: age, occupation, monthly income, medications (except antipsychotics) and comorbidities of hypertension, hyperlipidaemia and diabetes. This ‘propensity matching’ ensured that the differences in rates of breast cancer would not be due to differences in any of these variables.

The main exposures of interest were a first diagnosis of schizophrenia and prescription of antipsychotics between 1998 and 2008. The outcome was diagnosis of breast cancer by the end of 2011. The authors also conducted secondary analyses of type of antipsychotic medication and risk of breast cancer. This was to test the hypothesis that the antipsychotics most strongly associated with hyperprolactinaemia (second-generation antipsychotics and more specifically risperidone, paliperidone and amisulpride) would confer increased risk of breast cancer compared with first-generation antipsychotics.

What this paper adds

• Women with schizophrenia have nearly a twofold increased risk of breast cancer compared with those without schizophrenia (adjusted HR (aHR) 1.94, 95% CI 1.43 to 2.63).

• Women with schizophrenia aged under 50 are over twice as likely to develop breast cancer compared with women in the same age group but without schizophrenia (aHR 2.14, 95% CI 1.43 to 3.21).

• A combination of first-generation and second-generation antipsychotics is associated with higher breast cancer risk than either antipsychotic group alone. Risperidone, paliperidone and amisulpride do not increase risk over and above that conferred by a diagnosis of schizophrenia and use of antipsychotics (aHR 0.97, 95% CI 0.64 to 1.49).

Limitations

• Relevant risk factors for breast cancer, such as parity, breast feeding, menopausal status, obesity, physical activity, diet and smoking, were not assessed.

• The outcome relies on health professionals detecting and recording breast cancer. It is known that women with schizophrenia are less likely to attend breast screening than their non-schizophrenia counterparts² and diagnosis is often delayed.³ This means that rates of breast cancer in this study may have been underestimated in the schizophrenia group.

• The group of women with schizophrenia included a high proportion of employed individuals, including those working in white-collar jobs. This is atypical of most schizophrenia populations. Thus, the results may not be generalisable to other populations of women with schizophrenia.

What next in research

Where possible, large-scale studies should collect data on parity, menopausal status, smoking, Body Mass Index and physical activity level in order to account for the effect of these variables on risk of breast cancer in women with schizophrenia. These variables are now being recorded more frequently in major health databases as the importance of physical health in people with schizophrenia is recognised.

Many adverse health behaviours that increase risk of cancer, such as smoking, low physical activity and poor diet, are also risk factors for cardiovascular disease—the main cause of premature mortality in people with schizophrenia.⁴ However, as public health interventions that are effective for reducing unhealthy behaviours in the general population often fail to reach people with schizophrenia,⁵ research is needed into how to improve and sustain healthy living in this group.

Do these results change your practices and why?

Yes. This study highlights the need to collaborate with patients with schizophrenia around breast screening and breast self-examination, particularly in younger women.

Psychiatrists should promote patients’ engagement with primary care and regular health services in order to improve rates of cancer screening.

Concern about breast cancer risk should not stop psychiatrists from prescribing second-generation antipsychotics, as these do not appear to confer increased risk compared with first-generation antipsychotics.