A study of women who took estrogen for about six years and then stopped has found they were less likely to develop breast cancer and die from the disease than those who never used hormone replacement therapy.
The follow-up study of more 7,500 women from the Women’s Health Initiative trial found women who took the oral estrogen-only treatment were more than 20% less likely to develop breast cancer and remained significantly less likely to die from the disease almost five years after stopping treatment.
The results of the study have been published online in the journal The Lancet Oncology. They contradict the findings of a previous study that suggest there is a definitive link between hormone therapy and the risk of breast cancer.
Taking estrogen alone, however, still carries an increased risk of blood clots and stroke. And the decreased risk of breast cancer was not found among women with a family history of the disease, or with benign breast cancer.
“These latest results should provide reassurance about breast safety of estrogen use for durations of about five years for women with a hysterectomy seeking relief from postmenopausal symptoms,” said lead author Garnet Anderson, from the Fred Hutchinson Cancer Research Center in Seattle.
In 1993, the Women’s Health Initiative trial of estrogen was established to investigate the effects of conjugated equine estrogen on chronic disease. Nearly 11,000 postmenopausal women aged 50 to 79 who had previously had a hysterectomy received estrogen or a placebo for almost seven years. The trial was stopped in 2004 - earlier than planned - because of an increased risk of stroke and blood clots.
In this new analysis, the researchers have reported the overall effects of estrogen use on breast cancer rates and mortality after an extended follow-up of 7,645 women (78% of the original surviving members), who were tracked from March 2005 until August 2009.
The researchers found there was a 23% reduction in the incidence of invasive breast cancer compared with women who took the placebo. Among women in the estrogen group who did develop breast cancer, there was a 63% reduction in deaths from the disease compared with those in the placebo group.
The lower risk of breast cancer was restricted to women without a history of benign breast disease or a strong family history of breast cancer.
The team cautioned: “Our data do not support the use of estrogen for breast cancer risk reduction in light of the lack of benefit noted in populations at higher risk (including those with a strong family history of breast cancer or benign breast disease) and the additional risk of stroke and blood clots.”
Jane Elliott, president of the Australasian Menopause Society (AMS) and a lecturer in obstetrics and gynaecology at the University of Adelaide, said the results were reassuring for Australian women, many of whom use hormone replacement therapy for up to five years.
“It is also encouraging that the study found the protective effect of the therapy extended for years after women stopped taking it,” Dr Elliott said. “But we note that the lower risk of breast cancer was restricted to women without a history of benign breast disease or a strong family history of breast cancer, and the study used one particular oral form of estrogen.
"Findings only apply to women with a hysterectomy as those without a hysterectomy are not usually prescribed estrogen-only treatment; instead progesterone is added to the estrogen to prevent womb cancer.
It was disappointing, however, that the report came amid a sharp reduction in the number of hormone replacement therapy options for Australian women, she said. Last month, 12 current and past presidents of the AMS wrote to Catherine King, the Parliamentary Secretary for Health and Ageing, to express concern about the limited options for women suffering from disabling symptoms.
The letter warned that some women were resorting to untested medicines because they could not get proven products at an affordable price.
"Estrogen implants are no longer on the market and an Australian-developed estradiol transdermal spray has been approved by the [Food and Drug Administration] in America but is not approved for use here,” Dr Elliott said.