The study also included starting with letrozole and switching to tamoxifen, Coates noted.
"The difference between straight letrozole and the reverse sequence was very small in all groups, which will be reassuring to those women who, having started adjuvant treatment with letrozole, are obliged for any reason to discontinue that drug. Our data suggest that they can safely switch to tamoxifen if required with little or no harm to their prognosis," he said.
Both drugs are used after initial treatment to prevent the cancer from returning. The medications work by preventing the production or activity of estrogen, which is associated with breast cancer recurrence in postmenopausal women. The drugs work differently, which may account for the benefit of letrozole over tamoxifen. Letrozole is from a class of drugs called aromatase inhibitors, which block the production of estrogen. Tamoxifen differs in that it interferes with the activity of estrogen, not the hormone's production.
Dr. Victor Vogel, national vice president of research at the American Cancer Society, believes that because letrozole is more effective and has fewer side effects than tamoxifen, it should be used for most patients.
"The message to lay people is letrozole is better. That's the unequivocal, unconfused message," Vogel said. "If you are a postmenopausal women taking tamoxifen for early breast cancer, it's probably a good idea to switch from tamoxifen to letrozole."
However, tamoxifen should be used for patients who find it difficult to take letrozole, Vogel said. "Somewhere between 15 and 25 percent of patients get significant muscle aches and joint aches with aromatase inhibitors. For those patients, tamoxifen is still a reasonable thing to do."
Dr. Larry Norton, deputy physician-in-chief of Breast Cancer Programs at Memorial Sloan-Kettering Canc
All rights reserved