Late Use of Aromatase Inhibitor Still Effective Against Breast Cancer

By Sherry Baker
HealthDay Reporter
Tuesday, March 11, 2008; 1:00 PM

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TUESDAY, March 11 (HealthDay News) -- There's good news for the 60 percent of women with breast cancer whose malignancies are estrogen-driven: Researchers say taking the aromatase inhibitor (AI) drug letrozole (Femara) can cut risk of a recurrence by more than half.

That benefit was seen even when women initiated the drug one to seven years after they stopped treatment with the anti-estrogen drug tamoxifen, the study found.

In other findings, letrozole lowered the risk of breast cancer metastasis by 61 percent, according to the researchers. The drug also reduced the odds of a tumor forming in a breast that was initially cancer-free by more than 80 percent, said a team reporting in the April issue of the Journal of Clinical Oncology.

"We were expecting letrozole to work from the earlier, initial results, but the actual magnitude of benefit was a bit surprising. For any woman who has had hormone-sensitive breast cancer in the past, our results show a big reduction in recurrence if letrozole is initiated any time between 1 and 7 years after 5 years of tamoxifen -- that's up to 12 years after diagnosis," said lead researcher Dr. Paul E. Goss, director of Breast Cancer Research at Massachusetts General Hospital Cancer Center, Boston.

The findings are expected to be applied immediately to receptor-positive breast cancer treatment, Goss said.

There was one slight down side to letrozole therapy: Just over 5 percent of the 1,500 women taking the drug reported a new diagnosis of osteoporosis or bone fracture, compared to about 3 percent of 800 study participants who were not on the regimen, the researchers said.

Tamoxifen, which blocks estrogen receptor cells, is standard adjunct treatment for estrogen-sensitive cancers, but the benefits of the drug drop significantly after five years. Aromatase inhibitors block the other, less potent sources of estrogen in the body by keeping androgens from the adrenal glands and other tissues from transforming into estrogen.

The current study was based on data collected from the original MA.17 trial, conducted through the National Cancer Institute of Canada and also led by Goss. MA. 17 was designed to study whether letrozole could reduce tumor recurrence and increase survival in breast cancer patients after five years of tamoxifen treatment.