Breast cancer patients who follow up tamoxifen treatment with letrozole, an estrogen suppressor, cut risk of recurrence by nearly half, according to a study published online Thursday by the New England Journal of Medicine.
The study involving more than 5,000 women with the most common form of breast cancer was suspended halfway through its planned five-year timespan because of the surprisingly strong results. The journal also moved up publication of the study, which will appear in the Nov. 6 issue, because of the importance of the findings.
Cutting the study off early prevented more substantive long-term findings but gave all its participants the option of immediately starting letrozole treatment, according to the journal article and two accompanying editorials. Other breast cancer patients also could start on letrozole when they finish tamoxifen treatment.
“It is likely that in the coming months there will be much debate over whether the data and safety monitoring committee made the best decision” in halting the study, said one of the editorials, titled “Letrozole after Tamoxifen for Breast Cancer - What is the Price of Success?” by Dr. Norman Wolmark.
“At a minimum, suitable patients must be apprised of these important observations and must be given the opportunity to receive letrozole, with an understanding of the limitations of the data,” it concluded.
The study found that women with estrogen-sensitive breast cancer who had completed five years of tamoxifen treatment and then took letrozole were about 40 percent less likely to have the cancer return or get a new tumor in the other breast than those who received a dummy pill after tamoxifen.
“The estimated magnitude of the benefits ... was substantially greater than expected,” Wolmark wrote.
Estrogen fuels the growth of about half of all breast cancers, especially those in older women. Tamoxifen, the top hormonal treatment for estrogen-fueled tumors, is given to almost all such U.S. patients after surgery to help prevent breast tumors from returning.
In addition, when breast cancer returns and spreads, tamoxifen is the top treatment to stall tumor growth and buy women some time. It prevents estrogen from linking up to a receptor on the surface of cancer cells.
However, a previous study showed tamoxifen’s effectiveness ended after five years of use.
Letrozole, made by Novartis Pharmaceuticals, is an aromatase inhibitor that blocks production of estrogen. Side effects include increased risk of osteoporosis, hot flashes, night sweats, and pain in the bones, joints or back.
The study was conducted by 18 doctors from various Canadian, U.S. and European hospitals, universities and cancer centers.