Research summary
April 2006
New research confirms oestrogen-only HRT not associated with an increased risk of breast cancer
Summary
New findings released from a major American study known as the Women’s Health Initiative (WHI) have confirmed oestrogen-only hormone replacement therapy (HRT) is not associated with an increased risk of breast cancer. These findings were published in the 12 April issue of the Journal of the American Medical Association.
The WHI is a study focusing on strategies for preventing heart disease, breast and colorectal cancer and fracture in post-menopausal women. This 15-year project involves over 161,000 women aged 50-79.
The section of the study looking into the effects of oestrogen-only HRT involved 10,739 post-menopausal women who had undergone a hysterectomy. After seven years of follow-up there was found to be no increased risk of breast cancer.
National Breast Cancer Centre comment
It is important to note that oestrogen-only HRT is only suitable for women who have undergone a hysterectomy as it is associated with an increased risk of cancer of the uterus or womb.
Women requiring HRT who still have a uterus would be prescribed combined HRT because the progesterone protects the uterus from cancer.
While oestrogen-only HRT is not associated with an increased risk of breast cancer it is associated with other side effects such as an increased risk of stroke and blood clots.
These findings about oestrogen-only HRT should not be confused with the results released from a different section of the WHI study in 2002. The results released in 2002 attracted significant media coverage when researchers announced women taking combined HRT – that is a combination of oestrogen and progesterone – have an increased risk of breast cancer.
This 2002 study found that if we followed two groups of 1000 women in their 50s for a period of five years – one group who took combined HRT and another group that did not take any HRT:
- 11 women would develop breast cancer in the group that did not take HRT
- 15 women would develop breast cancer in the group that took combined HRT
In other words, there would be 4 additional cases of breast cancer in the group of women who took combined HRT.
Women considering taking any form of HRT should speak to their GP about the risks and benefits associated with the various options based on their individual situation.