Pittsburgh, PA - An analysis of the large Women's Health Initiative (WHI) has shown that statin use is not associated with an increased risk of breast cancer. Interestingly, the investigators did find that hydrophobic statins—a group that includes simvastatin, lovastatin, and fluvastatin—were associated with an 18% lower risk of breast-cancer incidence, although this finding needs to be confirmed in other studies, they add.

"Our results, taken together with the existing literature, indicate that breast-cancer risk is at least not increased in statin users," writes lead investigator Dr Jane Cauley (University of Pittsburgh, PA) in the May 17, 2006 issue of the Journal of the National Cancer Institute. "Whether or not statin use is associated with reduced breast-cancer risk is less certain. In the current study, after adjustment for breast-cancer risk factors, statin users had a somewhat lower breast-cancer incidence than nonusers. However, the differences were statistically significant only in women who reported using hydrophobic statins."

The data appear to support findings observed in an analysis of the Nurses' Health Study, previously reported by heartwire, which showed that the use of lipid-lowering medications, regardless of duration, was not associated with an increased risk of breast cancer. There had been some concern about the risk of cancer associated with statin use, with some studies showing a positive association, although other reports on the relationship between statin use and breast-cancer risk were mixed. In addition to the conflicting results, there is also some evidence to suggest that statins might inhibit tumor development, note the authors.

In the present study, Cauley and colleagues examined the association between the potency, duration, and type of statin used and invasive breast-cancer risk among 156 351 women enrolled in the WHI, of whom 7.5% were taking statin medications. The WHI includes an observational study and clinical trials of hormone therapy, dietary modification, and/or calcium and vitamin-D supplementation in postmenopausal women of different races and ethnicities.

Over an average follow-up of 6.7 years, the incidence of breast cancer was 4.09 per 1000 person-years among statin users and 4.28 per 1000 person-years among nonusers, or approximately 4.4% lower among those taking statins. In a multivariable-adjusted model, the risk of breast cancer was 9% lower among statin users, although this lower risk was not statistically significant. There was no trend in risk by duration of statin use or for any one particular statin. In addition, the use of postmenopausal hormone therapy did not modify the association between statin use and breast cancer.

Regarding the finding that there was a significant reduction in the risk of breast cancer among women taking hydrophobic statins, Cauley and colleagues note that this is consistent with a previous culture study showing that only the hydrophobic statins had an anticancer effect. As to why this finding was observed, the investigators write that some animal studies have shown that hydrophobic statins may induce apoptosis. They stress, however, that these findings warrant further study.