Tamoxifen had some troubling side effects: Longer use nearly doubled the risk of endometrial cancer. But it rarely proved fatal, and there was no increased risk among premenopausal women in the study — the very group tamoxifen helps most.
"Overall the benefits of extended tamoxifen seemed to outweigh the risks substantially," Dr. Trevor Powles of the Cancer Centre London wrote in an editorial published with the study.
The study was sponsored by cancer research organizations in Britain and Europe, the United States Army, and AstraZeneca PLC, which makes Nolvadex, a brand of tamoxifen, which also is sold as a generic for 10 to 50 cents a day. Brand-name versions of the newer hormone blockers, aromatase inhibitors, are $300 or more per month, but generics are available for much less.
The results pose a quandary for breast cancer patients past menopause and those who become menopausal because of their treatment — the vast majority of cases. Previous studies found that starting on one of the newer hormone blockers led to fewer relapses than initial treatment with tamoxifen did.
Another study found that switching to one of the new drugs after five years of tamoxifen cut the risk of breast cancer recurrence nearly in half — more than what was seen in the new study of 10 years of tamoxifen.
"For postmenopausal women, the data still remain much stronger at this point for a switch to an aromatase inhibitor," said that study's leader, Dr. Paul Goss of Massachusetts General Hospital. He has been a paid speaker for a company that makes one of those drugs.
Women in his study have not been followed long enough to see whether switching cuts deaths from breast cancer, as 10 years of tamoxifen did. Results are expected in about a year.
The cancer conference is sponsored by the American Association for Cancer Research, Baylor College of Medicine and the UT Health Science Center.
Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP