Enhanced cancer risk among patients with bipolar disorder

Background: In contrast to numerous epidemiological studies that explored the risk for cancer among persons with schizophrenic psychoses, analogous studies conducted on people with bipolar disorder are rarer, despite some commonalities in biological, treatment-related variables and unhealthy lifestyles. This study investigates the risk for cancer among psychiatric inpatients diagnosed with bipolar disorder. Methods: Linkage analysis was conducted based on the psychiatric and the cancer national databases. Standardized incidence ratios (SIR) for both aggregated sites and for breast cancer were calculated by comparing the incidence rates among hospitalized patients with bipolar disorder with the incidence rates in the Jewish-Israeli general population. Results: An enhanced cancer risk was found for bipolar disorder in both genders: men, SIR 1.59 (95% CI 1.01-2.17); women, SIR 1.75 (95% CI 1.31-2.18). The risk for breast cancer was higher, but not significantly, than in the general female population, SIR 1.70 (95% CI 0.99-2.41). Limitations: Our sample was derived from psychiatric inpatients, thus it is likely that the bipolar disorder cases had greater severity. Putative factors such as diet, smoking and medications were not investigated. Conclusions: Our study showed an enhanced risk for cancer among patients with bipolar disorder. Clinicians might note this risk for timely diagnosis and treatment.