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BACKGROUND: Endocrine therapy (ET) is a widely used treatment for breast cancer. In the UK, use is typically initiated in secondary care, with subsequent treatment in primary care. Evaluating use of ET depends on data sources containing accurate and complete information. This study aimed to evaluate the completeness and consistency of ET recorded in primary and secondary care data (SCD) and determine the value of combining data sources in describing use of ET. METHODS: This cohort study included women (50 + years) diagnosed with hormone receptor-positive invasive breast cancer in England, April-2015 to December-2019. Concordance of ET recorded in SCD and the Primary Care Prescription Database (PCPD) was evaluated. Factors associated with recording of ET in each setting were assessed using statistical models. RESULTS: Overall 110,529 women were included. 94% had ET recorded in either SCD or PCPD. ET captured in SCD varied from 3% (in Systemic Anti-Cancer Therapy data) to 52% (in the Cancer Outcomes and Services Dataset; COSD). By contrast, 93% of patients had an ET prescription in PCPD. Among patients with ET recorded, this was not captured in COSD for 45%. Capture in COSD was lowest for younger women, those with no comorbidity/frailty, with lower stage or HER2-positive disease, or with other treatments recorded. Overall concordance between COSD and PCPD was 57%, but varied substantially across NHS trusts (lowest decile≤28%; highest decile≥86%). Among women with ET recorded in both settings, the earliest record was in COSD for 97%; 59% of initial ET prescriptions recorded in COSD were not captured in PCPD. Combining PCPD and COSD data enabled estimation of ET duration. CONCLUSIONS: PCPD is vital for understanding the use of ET within this population. Completeness of SCD could be improved by ensuring information on first ET prescription is recorded. PCPD (linked to SCD) is a valuable resource for examining patterns of care for patients with cancer, including treatment duration and adherence.

Original publication




Journal article


Cancer Epidemiol

Publication Date





Endocrine therapy, Invasive breast cancer, Older patients, Primary care, Secondary care