Introduction: German epidemiologic cancer registries may store only encrypted personal identifiers. Thus, record linkage with secondary databases needs to be performed via procedures that are based on encrypted identifiers. In this paper, we describe the linkage of patient data from a statutory health insurance company (AOK NordWest) and from the Disease Management Program for diabetes mellitus type 2 with the database of the cancer registry. We report the cancer incidence in patients with type 2 diabetes (T2D).
Methods: Personal identifying variables of the patient cohort were encrypted before being sent electronically to the cancer registry and submitted to a probabilistic record linkage with registry data. The study included T2D patients who were residents of the Münster, Detmold, or Arnsberg districts and who were aged 40-79 years. Only primary cancers occurring between the date of enrolment and the censoring date (31 December 2010) were included. The standardized incidence ratio (SIR) was calculated relative to the number of incident cases expected on the basis of the averaged incidence rates in the general population.
Results: The record linkage took about 3 weeks of processing time. A total of 67,447 T2D (49.2 % men) cases were included for analyses. Incident cancer was diagnosed in 2,086 men and 1,578 women. Cohort members showed an elevated risk for cancer of the liver (SIR =1.86; 95% CI =1.47-2.31), pancreas (SIR = 1.62; 95 % CI =1.36-1.91), lung (SIR = 1.21; 95% CI 1.11-1.32), and uterus (SIR = 1.34; 95 % CI 1.08-1.65), and they were less likely to be diagnosed with prostate cancer (SIR =0.72; 95% CI = 0.65-0.79).
Discussion: The findings of this study suggest that record linkage of secondary databases with cancer registry data for research purposes can be effectively carried out in compliance with strict data-protection regulations.