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Cholesterol-lowering drugs not associated with increased breast cancer risk

May 17, 2006

PITTSBURGH- A report being published in the Journal of the National Cancer Institute found that women who took statins-the widely used cholesterol lowering drugs-do not face an increased breast cancer risk as had been suggested by some previous studies. In fact, the study, which was led by a researcher at the University of Pittsburgh Graduate School of Public Health (GSPH), found that women who took hydrophobic statins, named for their inability to dissolve readily in water, had an almost one-fifth lower incidence of invasive breast cancer compared to women who did not take statins.

"At minimum, our findings suggest that women can now be reassured that they are not increasing their risk of developing breast cancer by taking these drugs," said senior author Jane Cauley, Dr.P.H., professor and vice chair for research, department of epidemiology, GSPH. "Although we found that women who took hydrophobic statins actually lowered their breast cancer risk, we believe this finding needs to be confirmed in additional studies."

Dr. Cauley and her co-workers, representing several other research institutions, obtained their findings by analyzing breast cancer incidence over an almost seven-year period among more than 156,000 women enrolled in the long-running Women's Health Initiative study. Of this group of post-menopausal women, 11,710 were statin users; with about 30 percent taking a hydrophilic, or water soluble, statin, and the remaining 70 percent taking a hydrophobic statin.

During the follow-up period, 4,483 women in the study were diagnosed with invasive breast cancer. When the research team examined statins as a class, they found no statistically significant association between statin use and breast cancer incidence, although statin users did tend to have somewhat lower breast cancer rates than non-statin users. Breast cancer incidence also was not associated with how long statins were used. Moreover, use of post-menopausal hormone therapy did not modify the association between statin use and breast cancer. However, when the investigators analyzed breast cancer rates by type of statin, they found that among women taking any of several hydrophobic statins, there was an 18 percent decreased incidence of breast cancer compared to nonusers of statins and that this difference was statistically significant.

Dr. Cauley notes that finding a link between hydrophobic statins and reduced breast cancer risk is consistent with the results of several other recent studies. One, a cell culture study, found that hydrophobic statins inhibited the growth of several breast cancer cell lines, while a hydrophilic statin did not. In addition, another study reported a 72 percent lower risk of breast cancer in a small group of women, most of whom were taking hydrophobic statins.

"A number of different mechanisms have been identified by which this class of statins might inhibit the growth of cancer. For example, animal studies have shown that hydrophobic statins induce programmed cell death, or apoptosis. Hence, there certainly is some biological plausibility for this class of statins preventing cancer," said Dr. Cauley.

However, she cautions that further research is needed to determine whether hydrophobic statins actually can inhibit breast cancer in humans.

Statins are among the most widely prescribed drugs in the United States, with $12.5 billion in annual sales. In 2004, two statins - atorvastatin and simvastatin - were the No. 1 and No. 2 best-selling drugs in the country, with sales of atorvastatin alone topping 70 million prescriptions. Although highly effective in reducing cholesterol, statins have side effects, including headache, nausea, vomiting, constipation, diarrhea, rash, weakness and muscle pain. The most serious side effects, although rare, are liver failure and permanent muscle damage.

University of Pittsburgh Medical Center