Sept 6, 2007 -- Nearly half of women on certain antiestrogen drugs that can help keep breast cancer at bay develop aches and pains so severe that the women stop taking their medication, a new study suggests.
The drugs, known as aromatase inhibitors, block an enzyme the body uses to make estrogen, which fuels some breast cancers. Given after surgery, chemotherapy, or radiation therapy, the drugs substantially slash the risk of recurrence.
"We were surprised at the large number of women who stopped taking the drugs due to musculoskeletal symptoms," says N. Lynn Henry, MD, PhD, a lecturer in internal medicine at the University of Michigan Medical School in Ann Arbor.
"Only 15% of patients in other studies stopped taking aromatase inhibitors for any side effect and here we have nearly 15% dropping out because of musculoskeletal problems alone," she tells WebMD.
Drug Side Effects
Overall, 23% of the women in the new study given one of two aromatase inhibitors -- Aromasin or Femara -- stopped taking their drugs due to side effects, which also included hot flashes and nausea, Henry says.
Henry says that most women told their doctor about the problem and were switched to a different aromatase inhibitor or tamoxifen, an older antihormone drug.
"At least with the very small numbers we have at this point, the women seem to be tolerating the new drug after the switch," she adds.
The study included 100 postmenopausal women on Aromasin or Femara who filled out questionnaires asking about pain and difficulty with daily activities.
Forty-two percent of the women reported serious bone and joint problems, such as severe pain or difficulty opening a jar, and were referred for evaluation by a rheumatologist. The symptoms struck an average of two months after they started taking the drug.
The researchers did not compare the rate of side effects between Aromasin and Femara.
Henry says that there does not seem to be any way, at least at this point, to predict who will develop serious aches and pains. Results showed that older women are as susceptible as younger ones, and overweight women as susceptible as thinner women.
Aromatase Inhibitors Still Drugs of Choice
Julie R. Gralow, MD, an associate professor of medical oncology at the University of Washington School of Medicine and moderator of a press briefing on the findings, says that at least for now, the findings should not deter doctors from recommending aromatase inhibitors.
"Tamoxifen is a good drug, but it also has side effects, and the aromatase inhibitors have consistently been shown to improve survival compared with tamoxifen alone," she tells WebMD.
"We may be able to manage the pain with lifestyle changes or medication such as nonsteroidal anti-inflammatory drugs," he tells WebMD.
Diane Young, MD, vice president of global medical affairs at Novartis Pharmaceuticals, maker of Femara, says that studies in tens of thousands of women taking Femara or other aromatase inhibitors have shown a lower risk of musculoskeletal complications than in this study.
"This is an excellent study and we definitely support research to try to better characterize side effects. But we can't say the drop-out rates are increasing as the numbers here are relatively small and follow-up is not that long," she tells WebMD.
Susan Snodgrass, MD, RPh, medical director of Pfizer Global Oncology, which makes Aromasin, says, "Side effects relative to musculoskeletal pain with aromatase therapy are a class effect, and have been well established.
"As evident through its sponsorship of this study, Pfizer is committed to patient safety and fully supports continued research regarding the side effects of Aromasin and all breast cancer treatments," she tells WebMD.
In addition to Pfizer, the National Institutes of Health, and Novartis provided funding for the study.