Women who choose hormone replacement therapy after menopause may be at greater risk of certain kinds of breast cancer, according to a US study.
The Iowa Women's Health Study followed 37,105 postmenopausal, women for 11 years to see whether HRT increases the risk of three different types of breast cancer: benign lesions of the ducts, highly malignant cancers of the ducts or lobes, and invasive cancers with "favourable prognosis", an uncommon but doctors claim highly treatable form of cancer.
The use of HRT seemed to mainly increase the risk of invasive cancers with favourable prognosis. Women who used HRT for five years or less were 1.81 times more likely to have this slow growing, supposedly curable cancer than women who never used hormones. Those who had used hormones for more than five years were 2.65 more likely to have this type of tumour.
Although other studies have shown a small increase in the risk of breast cancer with long term hormone use, this is the first to show that the risk varies among different types of breast cancer (JAMA, 1999; 281: 2091-7).