Can taking aspirin uncover asymptomatic bladder cancer?

The presence of blood cells in urine is a sign of bladder cancer Because aspirin blocks platelets from forming harmful blood clots, the medication can cause mild bleeding or worsen existing bleeding in the urinary tract. Results from a study in the Journal of Internal Medicine suggest that this may prompt a clinician to run tests that uncover an asymptomatic bladder tumor.

For the study, investigators analyzed information on 50,771 Danish adults who started taking aspirin in 2005–2023, as wells as 156,191 who started non-aspirin non-steroidal anti-inflammatory drugs (NSAIDs), which have less pronounced antiplatelet abilities than aspirin.

Compared with adults from the general population who have never used aspirin or NSAIDs, aspirin initiators received more cystoscopies—minimally invasive procedures that allow a doctor to view the inside of the bladder and urethra with a lighted tube equipped with a camera. Cytoscopy results showed that recent aspirin initiators had a similar bladder cancer prevalence, but a lower prevalence of invasive stage compared with never-users. This suggests that individuals initiating aspirin treatment represent a patient population with a higher incidence of bladder cancer, and that their higher cystoscopy rate reflects this and thus is clinically warranted. The combination of a larger proportion of relevant cystoscopies and a lower prevalence of invasive cancer stage at diagnosis may represent unmasking of otherwise asymptomatic bladder cancer.

NSAID initiators received more cystoscopies than never-users, but they had a lower bladder cancer prevalence after cystoscopy and a similar stage distribution as never-users. This suggests that the higher cystoscopy rate may not have been clinically warranted.

“We are very encouraged by these results. In the clinical setting, they underline the importance of acting on suspicious bladder cancer symptoms among aspirin initiators,” said lead author Malene Söth Hansen, MD, of Aarhus University. “The findings may further have implications for the question of whether aspirin can prevent bladder cancer, as detection in trials with short-term follow-up may appear as a higher incidence in the aspirin-exposed cohort.”

Reference:

Hansen MS, Dyrskjøt L, Heide-Jørgensen U, Jensen JB, Nørgaard M. Aspirin or non-steroidal anti-inflammatory drug initiation and subsequent bladder cancer evaluation. J Intern Med. 2026;1–11.