Linkage of the UK Clinical Practice Research Datalink with the national cancer registry

Excerpt

For some years, researchers working with primary care databases, such as the UK Clinical Practice Research Datalink (CPRD), have advocated linkage with other datasets speculating that this will enhance classification of exposures and outcomes. The article from McDonald et al. [1], focusing on CPRD, provides an updated review of studies offering empirical evidence to support the above advocacy. This is clearly illustrated with the example of classifying incident cancer. McDonald et al. [1] correctly cited the paper from Boggan et al. [2] that the level of concordance for “the recording of cancer cases between CPRD and cancer registries”—namely the National Cancer Registration and Analysis Service (NCRAS)—is 83.3% for all cancer types. However, in that study, the concordance varied by cancer type, being as low as 54% for non-melanotic skin cancers and 60% for kidney cancer. Taking this background further, Ranopa et al. [3] sought to explain why there might be differences in concordance, and through a systematic review (1998–2013), identified 84 studies with incident breast, colorectal, or prostate cancer as the diseases of interest. While the study captured data from several UK primary care databases in addition to CPRD, they demonstrated that where incident cancer was classified from GP entries (through READ codes), there was a lack of consistency in algorithms defining cancer diagnoses. For example, cancer code lists included in-situ carcinoma, and often grouped non-epithelial and epithelial malignancies from the same anatomic site as site-specific ‘cancer’. Furthermore, 27 studies used chemotherapy codes in GP records to supplement cancer classification, potentially biasing against identification of cancers where surgery or radiotherapy are the primary treatment modalities. …