TUESDAY, March 11, 2008 (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.
In October of 2003 , the study was ended a year earlier than originally planned when preliminary data showed that women taking letrozole were significantly less likely to have a cancer recurrence. Study participants in the placebo arm were offered letrozole when the study was halted. According to Goss, that gave the researchers the opportunity to compare the recurrence rates in women from the placebo group who chose to take the AI with those who decided on no further treatment.
Based on the new findings, "we believe every patient who has previously taken tamoxifen should discuss the findings of this study with her oncologist. Our results suggest if you take anti-estrogen, aromatase inhibitor therapy at any point of diagnosis, it is going to impact your chances of not experiencing a recurrence," Goss said.
Another expert agreed that the findings are significant.
"This study shows that the hormonal driving pathways continue to be very active after the tamoxifen has ended. And, the fact you've got a 60 percent improvement in disease-free survival with the addition of letrozole is a very powerful argument for its inclusion in treatment," said Dr. Brian Leyland-Jones, executive director of the Winship Cancer Institute at Emory University in Atlanta.
"The only imperfection of this trial, in terms of its design, is that it was not randomized -- patients chose whether or not to continue on letrozole," Leyland-Jones said. "And the only negative note is the risk of osteoporosis and increased risk of fractures for those who switched to letrozole. So, the news is very good but not all perfect."
More information
For more on breast cancer, head to the National Cancer Institute.
