SAN ANTONIO – Statin therapy had no effect on the incidence of breast cancer during 823,086 person-years of prospective follow-up in the Nurses’ Health Study, Thomas P. Ahern, Ph.D., reported at the San Antonio Breast Cancer Symposium.
“Our results indicate that cholesterol-lowering statin therapy neither increases nor decreases breast cancer incidence rate in postmenopausal women. Considering the latest report indicated an increased breast cancer risk among statin users, our neutral findings should reassure physicians that statin therapy for the prevention of cardiovascular disease is safe with respect to breast cancer risk,” declared Dr. Ahern of the University of Vermont, Burlington.
The new Nurses’ Health Study analysis included 79,518 postmenopausal women followed prospectively during 2000-2012. During that period 3,055 study participants were diagnosed with invasive breast cancer.
Statin users were older, had a higher mean body mass index, were more likely to have diabetes, were far more likely to undergo regular mammographic screening, and had greater usage of nonstatin cardiopreventive medications than never-users of statins. In a multivariate regression analysis adjusted for these potential confounding factors as well as for family history of breast cancer, menopausal hormone therapy, alcohol intake, physical activity, history of benign breast disease, and reproductive history, the incidence of breast cancer did not differ between current, never-, and ever-users of statins.
Nor was the risk of breast cancer affected by longer duration of statin use, as women on the lipid-lowering medication for 8 years or more had the same null risk as those who’d been on statin therapy for a shorter time.
In drilling down to examine the separate risks of invasive ductal or lobular breast cancer, estrogen receptor–positive or –negative cancer, and in situ breast cancer, the incidence of none of these histologic types differed according to whether a patient had been on a statin. Nor did it matter whether a woman had been on a hydrophilic statin, such as rosuvastatin or pravastatin, or a lipophilic one, Dr. Ahern continued.
The Nurses’ Health Study analysis was prompted by a case-control study reported 2 years ago by investigators at Fred Hutchinson Cancer Research Center in Seattle. They found an association between 10 years or more of statin therapy and increased risk of developing ductal and lobular breast cancer (Cancer Epidemiol Biomarkers Prev. 2013 Sep;22:1529-37). That report received wide publicity and caused considerable concern among women taking statins to reduce cardiovascular risk.
However, the Seattle study was much smaller than the Nurses’ Health Study. Moreover, the Seattle findings were at odds with numerous other studies as evidenced by the results of an earlier meta-analysis of seven randomized controlled trials and nine observational statin studies which showed no increased in breast cancer incidence associated with statin therapy (J Clin Oncol. 2005 Dec 1;23:8606-12).
In contrast to statin therapy’s neutral effect on primary breast cancer incidence, multiple studies have shown “a very consistent and robust protective association” between statin use and breast cancer recurrence, Dr. Ahern noted. These clinical studies are supported by laboratory evidence that statins interrupt growth of many different cancers, including breast cancer, he added.
Discussant Melissa L. Bondy, Ph.D., said, “We epidemiologists always think of the Nurses’ Health Study as the end-all and be-all, the gold standard for providing insight into an exposure that would have occurred before disease onset. I believe that we get really good information from these women who have been committed to participating in this study for many years.”
“The Nurses’ Health Study population is really well characterized and is in a strong position to answer this question about statins and breast cancer risk. So I think that we can put this question to rest. We can now say that this is the end-all study and it does not look like statins increase the risk of breast cancer. It’s an important finding,” observed Dr. Bondy, professor of cancer prevention and population sciences at Baylor Medical College, Houston.
Dr. Ahern and Dr. Bondy declared having no financial conflicts of interest regarding the federally funded Nurses’ Health Study.