Aims/hypothesis: Recent prospective studies found an elevated cancer risk shortly after diabetes diagnosis, and this was probably due to increased ascertainment. This study investigated whether site-specific cancer risks are also raised following enrolment in a disease management programme for type 2 diabetes mellitus (DMP-DM2).
Methods: We linked records from a DMP-DM2 to population cancer registry data. The study period was from June 2003 to December 2009. Standardised incidence ratios (SIRs) were calculated for time intervals following DMP enrolment using the cancer incidence rates of the general source population. Additionally, Poisson regression with natural splines was used to assess time-dependent cancer incidence by diabetes duration.
Results: There were 2,034 first invasive cancer cases identified over 163,738 person-years of follow-up. Pancreatic cancer risk was significantly increased mainly in the first year after enrolment (SIR 1.62); the increment was only seen for patients in whom diabetes had been diagnosed less than 1 year before DMP-DM2 enrolment. Risk of endometrial cancer was similarly raised in the first year after DMP-DM2 enrolment among individuals newly diagnosed with diabetes but decreased rapidly thereafter. There was no time dependence in the incidence of cancers of the liver, lung, colon, breast and prostate.
Conclusions/interpretation: Enrolment in a DMP-DM2 did not appear to induce ascertainment bias for most cancers. Cancer risks were initially increased, especially for pancreatic cancer, potentially as a result of reverse causality. Ascertainment bias and time-dependent incidence of cancer appear to be less of a problem in settings using DMP-like structures for the study of the association between diabetes duration, glucose-lowering medication and cancer incidence.