HRT study provides more evidence of bowel cancer risk reduction
Researchers at the University of Minnesota School of Public Health found have found more evidence that hormone replacement therapy (HRT) may reduce a woman's risk of bowel cancer.
The finding is based on an analysis of data from 56,733 postmenopausal women, all of whom took part in the 15-year follow-up study of the Breast Cancer Detection Demonstration Project.
960 women were diagnosed with bowel cancer over the course of the study.
Those who had used oestrogen-only hormone therapy at some stage in their lives, but who had stopped, still had a 17 per cent reduced risk of bowel cancer (relative to those who had never used HRT).
Those who were still taking HRT had a 25 per cent reduced risk, and those who had been taking it for ten or more years had a 26 per cent reduced risk.
Women who had used combined HRT (oestrogen and progestin) at some stage had a 22 per cent reduced risk, while those who had stopped taking oestrogen and progestin at least five years previously had a 45 per cent reduced risk.
Commenting on the findings, which are published in the journal Cancer Epidemiology, Biomarkers and Prevention, Jill Johnson, a doctoral student at the University of Minnesota School of Public Health, said: "Compared to women who had never taken these hormones, the use of oestrogen plus progestin was associated with a reduced risk of colorectal cancer."
Previous research has suggested that hormones may help to reduce the risk of bowel cancer by decreasing levels of insulin-like growth factors.
However, Ms Johnson noted that more research will be needed to determine the mechanism by which HRT apparently reduces bowel cancer risk.
A number of previous studies have also found evidence of HRT's protective effect against bowel cancer.
A meta-analysis by F Grodstein et al, published in the American Journal of Medicine in 1999, concluded that women who had ever used HRT were 20 per cent less likely to develop bowel cancer than those who had never used HRT, while those currently using HRT had a 34 per cent reduction in risk.
Meanwhile, a Canadian study published in the British Journal of Cancer in 2004 found that women who took oestrogen-only HRT may benefit from a significant reduction in risk, with trans-dermal HRT - which is administered via a skin patch - appearing to be the most beneficial form of delivery.
Dr Julie Sharp, Cancer Research UK's senior science information manager, said: "Hormone levels play an important role in cancer risk. This research confirms previous reports showing that HRT - particularly the combined form of HRT - can reduce the chance of getting bowel cancer. Scientists do not yet know how these synthetic hormones do this.
"But it is important for women to remember that HRT can also increase the risk of other cancers, including breast cancer. Any woman concerned about HRT and her personal cancer risk should talk to her GP."
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J. R. Johnson, J. V. Lacey, D. Lazovich, M. A. Geller, C. Schairer, A. Schatzkin, A. Flood (2009). Menopausal Hormone Therapy and Risk of Colorectal Cancer Cancer Epidemiology Biomarkers & Prevention, 18 (1), 196-203 DOI: 10.1158/1055-9965.EPI-08-0596