New opportunities for drug outcomes research in cancer patients: The linkage of the Eindhoven Cancer Registry and the PHARMO Record Linkage System

Background: Insight into co-morbidity and treatment effects is pivotal to improve quality of care for cancer patients. Objectives: To determine whether linkage of the Eindhoven Cancer Registry (ECR) and the PHARMO Record Linkage System (RLS) was technically feasible and to assess which patient-centric data would result from this linkage. Methods: The ECR records data on tumour stage and primary treatment of all newly diagnosed cancer patients in the southeastern Netherlands including co-morbidity at diagnosis, whereas the PHARMO RLS includes data from multiple linked observational databases such as data on drug utilisation (for both in- and out-patients, including chemotherapy), hospitalisations and clinical laboratory measurements. All patients who lived or had been living in the overlapping area served by the ECR and the PHARMO RLS during 1998-2006 were selected for linkage which was performed with probabilistic medical record linkage. Results: The linkage resulted in an ECR-PHARMO cohort of 40,004 cancer patients with a total of 42,767 primary tumours. The cancer patients in the linked ECR-PHARMO cohort were representatives for the cancer patients included in the total ECR during 1998-2006. Cancer patients included in the cohorts had a mean history of 5 years and a mean follow-up ranging from 2 to more than 4 years (dependent on the survival rate of the specific cancer type). Conclusions: Linkage of ECR and the PHARMO RLS creates the possibility to study patient-centric drug utilisation, health resources utilisation and their costs, in addition to the effectiveness and safety of pharmaceuticals in routine daily practice in cancer patients.