Aspirin or non-steroidal anti-inflammatory drug initiation and subsequent bladder cancer evaluation

Whether aspirin or non-aspirin non-steroidal anti-inflammatory drugs (NSAIDs) initiation may unmask unknown bladder cancers (BCs) by hematuria remains controversial.

To evaluate unmasking, we compared cystoscopy rates, BC prevalence at cystoscopy, and invasive stage prevalence at diagnosis in aspirin or NSAID initiators with never-users.

Using the Danish population-based registries, we identified all new aspirin or NSAID users in 2005-2023 and a matched never-using comparison cohort. Second, we identified all first-time cystoscopy recipients in 2005-2022 with aspirin or NSAID initiation within 1 year prior or never-use in 10 years preceding cystoscopy. Comparing these groups, we computed hazard ratios of cystoscopy during 1-year follow-up, prevalence ratios of BC at cystoscopy, and invasive stage disease at diagnosis.

Among 50,771 aspirin initiators (median age: 67 years, 51% men) and 156,191 NSAID initiators (age: 45 years, 50% men) adjusted hazard ratios of cystoscopy were 1.54 (95% confidence interval [CI]: 1.38-1.72) and 1.56 (95% CI: 1.43-1.70) compared with never-users. Cystoscopy recipients included 683 aspirin (age: 70 years, 69% men) and 1414 NSAID initiators (age: 60 years, 63% men); standardized morbidity ratio weighted (SMRW) prevalence ratios were 0.97 (95% CI, 0.76-1.22) and 0.65 (95% CI, 0.51-0.82) compared with never-users. The SMRW invasive stage prevalence ratios were 0.81 (95% CI, 0.63-1.03) and 1.07 (95% CI, 0.85-1.34) in the aspirin and NSAID comparison.

The combination of more cystoscopies and a lower prevalence of invasive stage at BC diagnosis may suggest the unmasking of asymptomatic BC in aspirin initiators. We did not find indications of unmasking with NSAID initiation.