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The most common medication used to treat type 2 diabetes is showing some potential that it may also inhibit breast cancer cell growth. Several studies found that diabetics who were treated with the oral drug metformin were less likely to develop cancer than those who did not take the medication. Increasingly, evidence is mounting that metformin not only reduces blood sugar and insulin levels, but also may improve breast cancer outcomes.
At the 2013 annual American Society of Clinical Oncology (ASCO) meeting researchers presented results of a "meta-analysis" that reviewed 47 articles published between 1966 and August 2012 related to metformin and cancer incidence. The analysis showed that cancer incidence was reduced by 43% in people taking metformin compared with other anti-diabetic medications; cancer mortality was reduced by 49%. The most notable cancer risk reductions were in liver, lung and breast cancer.
A clinical trial studying metformin to lower breast cancer risk in BRCA mutation carriers and other high-risk women is now open.
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Nonsteroidal anti-inflammatory drugs (NSAIDs) are medications used for pain relief. This category includes many common over-the-counter painkillers, such as aspirin, ibuprofen (Advil, Motrin) and naproxen sodium (Aleve). Several studies have tried to determine whether aspirin and other NSAIDs reduce breast cancer risk. The Women’s Health Initiative studied the use of NSAIDs by women over the age of 50. Those who used aspirin on a regular basis had a 21% decreased chance of developing breast cancer than women who did not regularly use the medication. Regular use of ibuprofen was associated with a 49% risk reduction in breast cancer risk. This lowered risk also applied to women with a family history of breast cancer (first-degree female relatives only: mother, sister or daughter). However, the study did not specifically focus on women who had BRCA mutations or had evidence of a hereditary breast and ovarian cancer syndrome.This study was “observational” only, meaning although women who regularly took NSAIDs were less likely to develop breast cancer, the study does not prove NSAIDs are responsible for the reduced risk of breast cancer. A clinical trial is needed to show that NSAID use lessens the risk for breast cancer.
Certain NSAIDs increase the risk for death from heart disease. A recent clinical trial studying whether Celebrex could lessen the risk for colon polyps was discontinued when there were more heart disease and heart-disease related deaths in participants who took the medication compared to participants who took a placebo. The risk was still low for death by heart disease: about 3% of people who were on the highest dose, and 2% risk for people on the lower dose. In that particular study, however, the benefits of Celebrex were not believed to outweigh the risks.
Clinical trials are looking at whether nonsteroidal anti-inflammatory agents can decrease breast cancer risk in high-risk women, including some studies looking at women with BRCA mutations. Results from this research will not be available for several years.
Statins are medications commonly used to lower cholesterol. A recent study showed women taking statins had a 51% reduction of breast cancer risk. This study was “observational” and “retrospective” only: although women who took statins on a regular basis were less likely to develop breast cancer, researchers cannot be certain that taking statins is responsible for the decreased risk. A clinical trial is needed in order to show that statin use lowers the risk for breast cancer.
Deslorelin is a medication that prevents the ovaries from producing estrogen. Research studies have shown that lowering estrogen levels through removal of the ovaries can lower the risk for breast cancer, particularly in women with BRCA mutations. Since Deslorelin prevents the ovaries from producing estrogen, there is reason to believe that it will also protect against breast cancer, however, unlike surgical removal of the ovaries, Deslorelin's effect on the ovaries is reversible: that means when a woman stops taking the medication, her ovaries will begin to make estrogen again. One preliminary study which studied the effects of Deslorelin on premenopausal women with BRCA mutations, showed that Deslorelin can decrease the density of breasts as seen on a mammogram. Increased breast density has been linked to breast cancer risk and also makes it more difficult for a radiologist to read mammograms of the breasts. Although this study is encouraging, more research is needed to show that Deslorelin lowers the risk for breast cancer.
Clinical trials are looking at whether Deslorelin can decrease breast cancer risk in high-risk women, including some studies looking at women with BRCA mutations. Results from this research will not be available for several years.
Fenretinide is a medication related to Vitamin A. Research studies suggest Fenretinide might reduce the risk of several types of cancers. Results of a 15 year Italian study on women who were already diagnosed with breast cancer showed that women who took Fenretinide for 5 years lowered their risk for a second breast cancer in the same or the opposite breast. Fenretinide seemed to work best on premenopausal women, with women under the age of 40 having a 50% reduction in risk for a second cancer. The protective benefit of Fenretinide continued even after women stopped the medication. Although the study suggests that Fenretinide lowers the risk of breast cancer, there is not enough research yet to say that Fenretinide can prevent breast cancer in high-risk women who have never had cancer. This study did not look exclusively at women with BRCA mutations, so it is unknown if the medication will be as effective for BRCA mutation carriers as it is for premenopausal breast cancer survivors in general. Fenretinide is not available in the United States.