The Pharmaceutical Journal
Vol 270 No 7255 p882
28 June 2003

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Both continuous and sequential HRT regimens increase breast cancer risk

The risk of breast cancer in women who use combined hormone replacement therapy (HRT) is increased whether they follow a continuous or sequential regimen, new research suggests (JAMA 2003;289:3254).

The risk associated with continuous HRT use is already documented (PJ, 13 July 2002, p43) but the effects of sequential use — a regimen commonly used in the United Kingdom — are largely unknown.

Dr Christopher Li, Fred Hutchinson Cancer Research Centre, Seattle, Washington, and colleagues examined the relationship between duration and patterns of HRT use and breast cancer risk in more than 2,000 women aged 65 to 79 years. They found that women who had taken combined HRT for longer than five years had double the risk of developing breast cancer and that risk increased with duration of use. "We found that both regimens [continuous and sequential] were associated with similar increases in breast-cancer risk. There does not seem to be any advantage to sequential progestin use compared with continuous progestin use with respect to reducing this risk," says Dr Li.

The researchers also found that combined HRT did not increase the risk of oestrogen-receptor negative or progestrogen-receptor negative breast cancers. "That the use of combined HRT only increased the risk of hormonally-positive tumours points to the importance of progesterone in breast-cancer development. It appears that HRT must contain progesterone to promote breast-cancer growth and that it may act through stimulation of both oestrogen and progesterone receptors, not just one or the other," explained Dr Li.