(HealthDay News) — Early detection bias may explain the pattern of increased bladder cancer risk previously reported in patients with type 2 diabetes, according to a study published online Aug. 29 in Diabetes Care.

Isabelle N. Colmers, from the University of Alberta in Edmonton, Canada, and colleagues used linked administrative databases (1996 to 2006) to create a cohort of 185,100 adults from British Columbia, Canada, with incident type 2 diabetes, who were age-, sex-, and index date-matched to individuals without diabetes in a 1:1 ratio. During annual time windows following the index date, the incidence rates and hazard ratios for bladder cancer were calculated.

During a median follow-up of four years, the researchers found that within the study population (54 percent men; average age, 60.7 years) 1,171 new bladder cancer cases were diagnosed. Bladder cancer incidence in the diabetes cohort was 85.3 per 100,000 person-years in the first year after diabetes diagnosis, compared with 66.1 in the control cohort (adjusted hazard ratio, 1.30; P = 0.03). The increased bladder cancer risk seen in the first year was limited to those with the fewest physician visits two years prior to the index date (≤12 visits, adjusted hazard ratio, 2.14; P = 0.003). Type 2 diabetes was not associated with bladder cancer after the first year.

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“The results suggest that early detection bias may account for an overestimation in previously reported increased risks of bladder cancer associated with type 2 diabetes,” the authors write.

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