National experts agreed yesterday that women who take estrogen after menopause increase their risk of developing cancer of the uterus eight-fold.
But the doctors and researchers summoned by the National Institutes of Health to issue a "consensus report," balked at making general recommendations about which women should take the drug.
Citing studies that show estrogen helps prevent "hot flashes" and bone loss, the conference chairman, Dr. Kenneth J. Ryan, said each woman and her physician must weigh such benefits against the known risk of cancer. "Patients have to make a value judgment of what they want," he said.
Estrogens have been prescribed for more than 20 years to millions of midddle-aged women for conditions ranging from "hot flashes" and thin vaginal tissues to broken bones. They have been promoted to retard ageing and alleviate mood swings, although there is no evidence that they do either.
Prescriptions for the female hormones peaked at almost 27 million in 1975 but since have fallen by 40 percent following publicity linking the drugs with uterine cancer. Last year, doctors wrote 16 million prescriptions, according to a national survey. The most prescribed brand is Premarin, manufactured by Ayerst Laboratories.
Since the risk of cancer of the uterus develops after a woman has been on estrogen for two years, the panel agreed the drug should be used in the lowest possible doses and for as short a time as practicable.
Estrogen, however, seems to prevent bone loss, "hot flashes" and thinning of vaginal tissues only as long as a women keeps taking it, said Dr. Isaac Schiff of Boston Hospital for Women. A Seattle study found that the average woman who takes estrogen after menopause stays on it for 10 years.
The report noted that the incidence of cancer of the uterus in the United States rose at the same rate as the prescribing of estrogens, and has begun to fall as prescriptions have declined.
No similar trend has been seen with breast cancer, but estrogens cause breast cancer in experimental animals, and scientists believe they may do so in humans.
Although only two of many studies found an increase in breast cancer among estrogen users, the report said the breat cancer issue "remains a concern."
Despite the risk of blood clots and heart attacks in younger women taking oral contraceptives, which usually contain estrogens, the hormones in older women have not been shown to increase blood clots, stroke or heart attacks, said Dr. Barbara S. Hulka, a University of North Carolina epidemiologist.
Nevertheless, Schiff said, women who have had any of these conditions, high blood pressure, cancer of the uterus or breast cancer, should not take the drug.
He added there is no evidence that estrogen creams are safer than pills, since new studies show they are absorbed through the skin. Creams have often been prescribed in the belief they had fewer side effects than the pills.