Atypical ductal hyperplasia "is a benign condition but it is a risk factor for breast cancer. It's not clear if it's a precursor to breast cancer," said Miglioretti, who is a senior investigator with the Group Health Research Institute in Seattle. "This sheds light on more of the breast process, how HRT affects breast cancer."
Miglioretti and her co-authors analyzed almost 2.5 million screening mammographies from samples provided by the Breast Cancer Surveillance Consortium. The mammograms were done between 1996 and 2005.
In 1999, atypical ductal hyperplasia was found in 5.5 per 10,000 mammograms but by 2005 had declined to only 2.4 per 10,000, a drop of more than half. This occurred despite an increase over time of rates of mammography, which tend to pick up the abnormality.
Meanwhile, breast cancer cases in women with atypical ductal hyperplasia declined from 4.3 per 10,000 mammograms in 2003 to 3.3 per 10,000 mammograms in 2005.
And postmenopausal use of hormone therapy dropped from 35 percent to 11 percent.
The study also revealed that cancers associated with atypical ductal hyperplasia tend to be less aggressive, lending support to the theory that less aggressive and more aggressive cancers develop differently, the authors stated.
One breast cancer expert said the new study dovetails with recent trends in breast cancer incidence.
"The finding they report is consistent with [previous] observations that suggested there was a drop in incidence of breast cancer in about 2003 and it coincided with when the Women's Health Initiative reported that estrogen-plus-progesterone use was associated with an increased risk of heart attacks as well as a slight increased incidence of breast cancer risk," said Dr. James Liu, chairman of obstetrics and gynecology at MacDonald Women's
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