Background: Symptoms reported by patients with undiagnosed genitourinary cancers may be confused with those of overactive bladder (OAB) syndrome.
Objectives: We studied incidence rates (IRs) of genitourinary cancers and other common cancers in initiators of antimuscarinic OAB drugs in the Danish national registries, overall and stratified by time since first prescription.
Methods: The study cohort comprised new users of oxybutynin, tolterodine, solifenacin, fesoterodine, trospium, or darifenacin (2004-2012), aged greater than or equal to 18 years, with no history of cancer before entry. Follow-up ended with cancer diagnosis, death, disenrollment, or end of study. Drug exposure was ascertained from the Danish National Prescription Registry, and cancer outcomes, from the Danish National Registry of Patients and the Danish Cancer Registry. IRs per 1,000 person-years and 95% confidence intervals (CIs) were estimated overall and by categories of months since cohort entry (MSCE) for each study cancer (bladder, breast, colorectal, lung, melanoma, non-Hodgkin lymphoma [NHL], pancreas, prostate, renal, and uterine).
Results: The study cohort included 72,917 patients (60% women, mean age at entry 66 years); 3,475 patients (1,832 men; 1,643 women) developed study cancers during 259,072 person-years. The most frequent study cancers were prostate (881; 25.4% of study cancers), breast (658; 18.9%), lung (534; 15.4%), colorectal (434; 12.5%), and bladder (369; 10.6%). The overall study cancer crude IR was 13.4 (95% CI, 13.0-13.9). Cancer IRs did not vary by OAB drug used. Bladder cancer IR (95% CI) was highest for less than 6 MSCE (4.2; 3.6–5.0), lower for 6 to less than 12 MSCE (1.3; 0.9–1.7) and thereafter. Prostate cancer IR was also highest for less than 6 MSCE (23.3; 20.8–26.0), lower for 6 to less than 12 MSCE (8.8; 7.3–10.6), and lower thereafter. Other cancer IRs did not show this effect of time since cohort entry.
Conclusions: Protopathic and/or detection bias are plausible explanations for higher IRs of bladder and prostate cancers in the first 6 months after starting OAB drug treatment. These findings are in line with results from other studies and must be considered in etiologic studies of OAB drugs and cancer risk.
