Risk of malignancy in patients with schizophrenia or bipolar disorder: nested case-control study

Abstract

Context: There is conflicting evidence on whether people with schizophrenia have a different risk of cancer from that of the general population.

Objective: To determine the risk of 6 common cancers in patients with schizophrenia or bipolar disorder.

Design: Population-based, nested, case-control study.

Setting: A total of 454 practices contributing to the QRESEARCH general practice database.

Participants: We analyzed 40,441 incident cases of 6 cancers (breast, colon, rectal, gastroesophageal, prostate, and respiratory) and up to 5 controls per case matched by single year of age, sex, general practice, and calendar time.

Main outcome measures: Odds ratios (ORs) for cancer risk associated with schizophrenia and bipolar disorder, adjusting for smoking, body mass index, socioeconomic status, comorbidities, and prescribed medications, including antipsychotics.

Results: For breast cancer, we identified 10,535/50,074 cases/controls; colon cancer, 5108/24,458; rectal cancer, 3248/15,552; gastroesophageal cancer, 3854/18,477; prostate cancer, 10,190/48,748; and respiratory cancer, 7506/35,981. After adjustment, patients with schizophrenia had a 190% increased colon cancer risk (adjusted OR, 2.90; 95% confidence interval [CI], 1.85-4.57), a marginal increased breast cancer risk (adjusted OR, 1.52; 95% CI, 1.10-2.11), and a 47% decreased respiratory cancer risk (adjusted OR, 0.53, 95% CI, 0.34-0.85). Patients with schizophrenia taking antipsychotics had a 308% increased colon cancer risk (adjusted OR, 4.08; 95% CI, 2.43-6.84). Patients with bipolar disorder had cancer risks similar to patients with neither condition after adjustment.

Conclusions: Patients with schizophrenia have a significantly higher risk of colon cancer and a lower risk of respiratory cancer compared with patients without schizophrenia after adjustment for confounders. In contrast, the risks of cancer in patients with and without bipolar disorder are similar, suggesting that residual confounding is unlikely to explain the findings. The increased risk of colon cancer is particularly marked in patients with schizophrenia who take antipsychotic medications.