Background: Cancer risks associated with the use of individual drugs to treat overactive bladder (OAB) are not known Objectives: In preparation for a postauthorization safety study for mirabegron, a drug with a novel mechanism of action to treat OAB, we assessed the risk for 10 common cancers in users of antimuscarinic OAB drugs.
Methods: We identified new users of tolterodine, solifenacin, fesoterodine, darifenacin and oxybutynin greater than or equal to 18 years old without cancer or HIV from the Swedish National Registers in years 2006-2012. We assessed two sex-specific composite cancer endpoints and the 10 individual cancers (lung/bronchus, colon/rectum, skin melanoma, bladder, non-Hodgkin lymphoma, kidney, pancreas, prostate, female breast, and uterus). We estimated age-sex-standardized incidence rates (IRs) per 1,000 person-years and 95% confidence intervals (CIs) for ever exposure to the study drugs overall and in strata of time since start of treatment.
Results: The cohort of 130,944 patients had a mean age of 66 years; 60% were women. The most commonly used OAB drugs were tolterodine, solifenacin and fesoterodine. During follow-up (mean 3.2 years), 5,653 patients (4.3%) were diagnosed with any of the study cancers, most frequently prostate (1,530; 27%), breast (961; 17%), or colorectal (888; 16%) cancer. For all study drugs combined, the IR (95% CI) for the composite endpoints was 10.0 (9.6-10.4) in women and 19.4 (18.7-20.1) in men. For each type of cancer, IRs were similar across individual drugs: prostate cancer, IRs ranged from 8.6 (6.2-11.0) for oxybutynin to 10.2 (9.4-11.1) for solifenacin; female breast cancer, 3.4 (2.7-4.1) for fesoterodine to 4.0 (3.3-4.7) for darifenacin; colorectal cancer, 1.6 (1.2-2.0) for fesoterodine to 2.4 (1.7-3.1) for oxybutynin. Some less common cancers had larger variations by individual drugs. IRs for bladder and prostate cancer were highest in the first 6 months after treatment start.
Conclusions: Based on age-sex standardized IRs, no antimuscarinic OAB drug seemed to carry increased cancer risks. IRs were higher during early treatment, driven by prostate and bladder cancer, which is consistent with protopathic bias or surveillance bias.
