A new study has found that the risk of progesterone receptor negative (PR-) breast cancer is greatly elevated among overweight or obese women who take statins to lower cholesterol. The study, which was conducted in Fargo, North Dakota, was restricted to postmenopausal Caucasian women without a history of using hormone replacement therapy. It included 95 women who were newly diagnosed with breast cancer and 94 cancer-free women who served as controls. Participant ages ranged from 55 to 81 years old.

No link was found overall between the use of statins and the risk of breast cancer. However, when stratified by cancer hormone receptor type, the risk of progesterone receptor negative (PR-) breast cancer was found to be four times higher for hydrophobic statin users than for non-users. Hydrophobic statins include Mevacor (lovastatin), Zocor (simvastatin), Lipitor (atorvastatin), Lescol (fluvastatin) and Baycol (cerivastatin). The authors conclude that the study found an increased risk of PR- breast cancer related to duration of statin use among overweight or obese postmenopausal women.

Study findings are surprising

The study findings are surprising because they appear to contradict previous studies that have reported that statins may protect against breast cancer (including PR- breast cancer) or are neutral with respect to risk:

  • A recent study found that Lipitor suppressed tumor growth and metastasis in mice with ER-/PR- human breast cancer grafts
  • Short-term treatment of women about to undergo surgery for DCIS or stage 1 breast cancer with Lescol has been shown to induce measurable reductions in tumor proliferation and increased apoptotic activity in high-grade tumors
  • A study using two animal models found that neither Lipitor nor Mevacor was effective in reducing the incidence of carcinogen-induced ER+ mammary carcinomas in rats or the development of ER- mammary tumors in transgenic mice
  • A study including 2,411 breast cancer patients in the Kaiser Permanente Northern California Cancer Registry found that the use of lipophilic statins such as Mevacor, Zocor, and Lipitor reduced the likelihood of ER-/PR- breast cancer
  • Study of women diagnosed with breast cancer in Wisconsin, Massachusetts, and New Hampshire between 1995 and 2001 found no association between overall statin use and risk of breast cancer.

The present study was relatively small, but it took into account several important factors. Overweight, postmenopausal women are far more likely to develop ER+/PR+ breast cancer than ER-/PR-, however they are more likely to develop ER+/PR- breast cancer than premenopausal women (although this type is far less common overall). A previous 2003 study reported that statin use increased breast cancer risk in women with long-term hormone replacement therapy exposure, but the present study excluded such women. Prior studies focused on ER status, not PR status. The reported size of the increase in risk of PR- breast cancer for overweight women in the present study is remarkable. Therefore, the results should be explained and followed up with additional studies rather than being rejected or ignored because they appear to contract previous results.