RCTs remain the gold standard for evaluation of drug efficacy and safety. However, the only way of identifying treatment pathways and improving understanding of costs and outcomes at different stages of care is via longitudinal observational studies. Observational data from electronic health records (EHRs) are increasingly being used to support pharmaco-epidemiological research.  Coverage, data quality and validity of UK EHR databases such as the Clinical Practice Research Datalink (CPRD) have improved in recent years, and many papers confirm the validity of data in diagnoses such as cancer. Published data show that recording of cancer diagnosis and mortality in primary care electronic records is generally consistent with Cancer Registry (CR) data in England. The use of “read codes” in CPRD to identify an event (cancer diagnosis or referral to secondary care) and the possibility of anonymous linkage to secondary care databases (e.g. Hospital Episode Statistics [HES] for information about hospital management as an in- or out-patient, to other CR data, and accurate mortality tracking by the Office for National Statistics [ONS]) allows the data and diagnosis to be validated against multiple sources, as well as identifying treatment pathways in both secondary and primary care. There are some limitations, e.g. not all patients identified in GP practices via the CPRD are linked to other databases.  Management data such as secondary care prescribing are difficult to access (not available in HES) but may be available from reviewing anonymized patient notes or by connecting to other datasets. For example, IMS Health links CPRD data with hospital pharmacy audit data and HES data. However these data have only become available recently, are expensive to access and currently patient population coverage is low. We will provide a detailed description of the possibilities for integrated database use to map treatment pathways for cancer patients.