Statistics show an increased rate of breast cancer in female patients with schizophrenia compared with the general population. Researchers in Finland conducted a nested case-control study to determine whether the increased risk could be attributed to antipyschotic treatment.
The researchers identified 1,069 women diagnosed with schizophrenia between 1972 and 2014 who were subsequently diagnosed with breast cancer between 1st January 2000 and 31st December 2017 (cases). Each case was then matched by age and duration of illness with five women without cancer (controls; n=5,339).
Significantly increased risk
The researchers found that five or more years' cumulative exposure to prolactin-increasing antipsychotics (eg, olanzapine, risperidone, haloperidol) was associated with a significant increase in risk of breast cancer (adjusted odds ratio [OR] 1.56 [95% CI 1.27 to 1.92]; p<0.001) compared with less than one year of exposure. Exposure to these drugs for one to four years was not associated with an increased risk.
Conversely, exposure to prolactin-sparing antipsychotics (eg, clozapine, quetiapine, aripiprazole) for one to four years, or for five or more years was not associated with an increase in breast cancer risk compared with exposure for less than 12 months (adjusted OR 0.95 [0.73-1.25] and 1.19 [0.90-1.58], respectively).
The study findings also suggest that long-term use of prolactin-increasing antipsychotics is associated with a greater risk of developing lobular adenocarcinoma than of developing ductal adenocarcinoma.
The researchers suggest that monitoring prolactinaemia and addressing hyperprolactinaemia is paramount in women with schizophrenia being treated with prolactin-increasing antipsychotics.