Do the benefits of taking a medication to prevent breast cancer outweigh the potential risks? That’s the question a new study published Monday in the journal Lancet Oncology is raising about exemestane, a cancer treatment that many scientists hope could also be used for breast cancer prevention.
Exemestane (also known by the brand name Aromasin) is currently used as an additional therapy to treat patients with breast cancer following the initial surgery to prevent the cancer from returning, and in women with advanced disease. It has also proven effective in significantly reducing (by 65 percent) the risk of developing breast cancer in post-menopausal women at high risk for the disease.
However, the Lancet study highlights a troubling side effect: use of the drug may also cause significant loss of bone mineral density or BMD, leaving a patient at increased risk for bone fractures and osteoporosis later in life.
Researchers looked at 351 women over a period of two years, and monitored BMD levels in the distal radius (the wrist joint) and the distal tibia (the ankle joint), among other parts of the body. When compared to women taking the placebo, the study found “exemestane worsens age-related decreases in bone mineral density by about three times, even in the setting of adequate calcium and vitamin D intake,” nutrients which promote bone health.
Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society, agrees with the study authors and the accompanying editorial that it is best to be cautious about using exemestane and other aromatase inhibitors for primary breast cancer prevention.
“In this study, they have not proven an increase in actual fractures, but if exemestane accelerates bone loss, then the possibility exists that it also increases the risk of fractures, which for older women can be debilitating and painful. The problem is, we do not yet know about the long term side effects of these drugs in women who would take them to prevent breast cancer.”
He also highlights another observation.
“We have to consider that this study only followed women for two years, but the treatment is supposed to go for five. Doctors and patients would likely be concerned about that amount of bone loss seen in a fairly short time in an otherwise healthy woman.”
Dr. Lichtenfeld wrote cautiously in his June blog entry about a study presented during the 2011 American Society of Clinical Oncology meeting which touted the preventive benefits of exemestane. He says for women who are at high risk, where breast cancer prevention strategies need to be considered, the treatment may be very beneficial.
“No-one is saying, ‘Do not use it,”’ Dr. Lichtenfeld explains, noting the drug is currently approved by the FDA for the treatment of postmenopausal women with estrogen-receptor positive early breast cancer following surgery to prevent the cancer from returning, or for women whose disease has progressed.
“The Lancet article and editorial suggest that you have to be very careful to understand the long term safety profile of this drug, and weigh the benefits and potential harms when used as a breast cancer prevention option. In that circumstance, many women who would take the drug never would have developed cancer in the first place; for these women it could potentially do more harm than good.”