Hydroxymethyl glutaryl coenzyme A inhibitors ('statins') are carcinogenic in rodents and an increased incidence of breast cancer was reported among pravastatin users in one randomised trial. We conducted a case -control study in the General Practice Research Database to evaluate the risk of breast cancer among 50-to 79-year old women treated with statins for hyperlipidaemia. Case and control women were matched by age, general practice, duration of prescription history in the General Practice Research Database, and index date. Adjusting for history of benign breast disease, body mass index, and use of hormone replacement therapy, women currently treated with statins had an estimated relative risk for breast cancer of 1.0 (95% confidence interval 0.6 -1.6) compared to women without hyperlipidaemia. Untreated hyperlipidaemia was associated with an increased risk of breast cancer (estimated relative risk 1.6; 95% confidence interval 1.1 -2.5). The estimated relative risk among women currently receiving only non-statin lipid-lowering drugs was similar to that of women with untreated hyperlipidaemia (1.8; 95% confidence interval 0.9 -3.4). We found no evidence for an increasing trend in breast cancer risk with increasing duration of statin use (median duration 1.8 years, maximum 8.6 years). (Newman and Hulley, 1996). Clinical trials focused on cardiovascular mortality and morbidity have had limited ability to assess the human carcinogenic potential of statins due to relatively short follow-up. Among 13 trials reporting cancer incidence and deaths as outcomes, with an average follow-up time of 3.3 years, no evidence was found of an overall increased risk of cancer (relative risk (RR) 1.03, 95% confidence interval (CI) 0.90 -1.17) or cancer deaths (RR 0.95, 95% CI 0.74 -1.21) among statin users (Hebert et al, 1997). However, concern was raised by the only study that reported on breast cancer risk, with 12 cases among pravastatin users and only one case in a placebo group of similar size (P=0.002) (Sacks et al, 1996).We used the General Practice Research Database (GPRD), an automated data source containing drug prescription and other medical information on more than 3 million residents of the UK, to study the possible relation of breast cancer to statin use and hyperlipidaemia.
MATERIALS AND METHODSWe conducted a matched case -control study on the risk of breast cancer in relation to use of statins, non-statin lipid-lowering agents, and untreated hyperlipidaemia among women aged 50 -79 diagnosed with breast cancer in 1992 -1998 in the UK General Practice Research Database (GPRD).
General Practice Research Database (GPRD)The GPRD started in 1988 and has been used extensively for research studies; the subset of data we have used during the past decade is of consistently high quality. (Jick et al, 1991) Some 350 practices contributed to data used in this report. In a previous study our group found that diagnoses of cancer are validated in 95% of cases for whom further information is obtained from general practitioners (Jic...