68 A new Danish study suggests that starting aspirin treatment may lead to earlier identification of hidden bladder tumours, as increased medical investigations are prompted by minor bleeding. Because aspirin inhibits platelet function and reduces the blood’s ability to clot, it can cause mild bleeding or exacerbate existing bleeding in the urinary tract. The presence of blood in urine is a known warning sign of bladder cancer, and findings published in the Journal of Internal Medicine on 1st June 2026 suggest that this bleeding may prompt clinicians to carry out tests that uncover previously asymptomatic tumours. Investigators analysed nationwide Danish registry data on 50,771 adults who began taking aspirin between 2005 and 2023, alongside 156,191 who started non-aspirin non-steroidal anti-inflammatory drugs (NSAIDs), which have less pronounced antiplatelet effects. Both groups were compared with matched individuals who had never used these medications. Aspirin users were significantly more likely to undergo cystoscopy within one year of starting treatment. These minimally invasive procedures allow clinicians to examine the inside of the bladder and urethra using a lighted camera. At cystoscopy, bladder cancer prevalence among aspirin users was comparable to that of non-users, but detected cancers were less likely to be invasive, suggesting that aspirin-related minor bleeding may help reveal tumours at an earlier stage. NSAID users also underwent more cystoscopies than non-users, but had a lower bladder cancer prevalence following examination and a similar stage distribution to non-users, indicating that the higher rate of investigation in this group 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 Søth Hansen of Aarhus University. “The findings may also 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.” The study authors emphasised the importance of appropriate follow-up for symptoms in this group and noted that further research could help clarify longer-term outcomes and any potential preventive effects. Bladder cancer is among the 10 most common cancers globally, with visible blood in the urine being its most significant clinical symptom. Aspirin is widely used for cardiovascular prevention, and while its link to urinary bleeding is relatively weak compared with stronger anticoagulants, the study highlights how even mild bleeding effects can influence diagnostic pathways. Previous research has explored aspirin’s potential role in cancer prevention, with some evidence of benefit in colorectal and other cancers through anti-inflammatory mechanisms. Associations with bladder cancer incidence have been less consistent, but this latest work adds nuance by suggesting that any observed increase in short-term studies could partly reflect improved detection rather than a true rise in risk. Experts emphasise that patients should not change their medication without medical advice. Anyone experiencing blood in the urine, whether taking aspirin or not, should seek prompt medical evaluation.