Recent research presented at EBCC-5 from the million women study found that taking Hormone Replacement Therapy (HRT) increased the risk of some types of breast cancer, but not others.
Scientists analysed the data from the UK study to try and find a link between HRT and the type of breast cancer that developed. The research found that women who took HRT had an increased risk of developing lobular cancer (affecting the cells in the ducts of the milk-producing glands) and tubular cancer. There was not such an increased risk of developing ductal breast cancer, the most common type of breast cancer that affects the cells lining the milk duct. There was no increase in the risk of medullary breast cancer, a kind of cancer that is common in women with a genetic predisposition to breast cancer.
The study demonstrated that women who had taken combined HRT (oestrogen and progesterone) had an even greater risk of developing lobular and tubular breast cancer than women on oestrogen only HRT. The researchers also discovered similar findings for women with breast cancer in situ - when the cancer has not spread to the surrounding tissues in the breast or other parts of the body. Women that took HRT had a significantly greater risk of developing lobular cancer in situ than ductal carcinoma in situ.
G. Reeves who presented the findings comments, "It is very interesting that HRT has different effects on different types of breast cancer. One possible explanation for the findings is that certain types of breast cancer are more likely than others to be hormone receptive. Further research into this topic could greatly help our understanding of the biological mechanisms underlying the development of breast cancer."
In 2003, the million women study confirmed that post-menopausal women taking combination HRT were twice as likely as non-users to develop breast cancer and women taking oestrogen-only HRT had a 30 per cent greater risk than those who haven’t taken HRT.
The increase in breast cancer risk starts within one to two years of beginning either form of HRT and increases the longer it is taken. As soon as HRT is stopped, the risk begins to fall and, after five years, is the same as for women who've never taken the drug. Combined oestrogen-progesterone HRT is usually prescribed for women who still have a uterus to avoid the increased risk of cancer of the uterus caused by oestrogen-only therapy. Women are advised to discuss their concerns with their doctor.