Cancer risk in persons receiving prescriptions for paracetamol: a Danish cohort study

The use of paracetamol has been associated with increased risks for urinary tract cancers and decreased risk for ovarian cancer, although results have been inconsistent. We conducted a population-based cohort study using data from the Prescription Database of North Jutland County and the Danish Cancer Registry. Cancer incidence among 39,946 individuals receiving prescriptions for paracetamol was compared with expected incidence based on the North Jutland population who did not receive paracetamol prescriptions, during a 9-year follow-up period. Standardized incidence ratios (SIRs) with corresponding 95% confidence intervals (95% CIs) were calculated for cancers overall and at selected sites. Overall, 2,173 cancers were observed with 1,973 expected, yielding a SIR of 1.10 (95% CI, 1.06-1.15). Significantly elevated SIRs were found for cancers of the esophagus (1.9; 95% CI, 1.3-2.8) and lung (1.6; 95% CI, 1.4-1.7). Nonsignificantly increased SIRs were observed for cancers of the liver (1.5; 95% CI, 0.96-2.2), renal parenchyma (1.3; 95% CI, 0.9-1.7) and renal pelvis/ureter (1.6; 95% CI, 0.96-2.6), whereas the SIR for cancer of the urinary bladder was close to unity (1.1; 95% CI, 0.9-1.4). For ovarian cancer, the SIR was close to expectation (0.9; 95% CI, 0.6-1.2) with no evidence of trends with duration of follow-up or number of prescriptions. A similar risk pattern was observed after exclusion of person-time experience following prescription for aspirin or other nonsteroidal antiinflammatory drugs in the study cohort and reference population. Our results do not support a major role for paracetamol in the development of cancers of the urinary tract, and we found little evidence of a protective effect of paracetamol against ovarian cancer. The elevated risks for cancers of the esophagus, lung and liver are most likely a result of confounding variables, but may warrant further investigation.