Editor—The fall in breast cancer deaths in women aged 40-54, first diagnosed under age 50 during 1991-2000, but not invited for screening, could be due to the reduction in the use of oral contraceptives and hormone replacement therapy after warnings of increased risk of thrombosis.1
In 1995-6 several large studies confirmed an increased risk of primary thrombosis of four to six times with different combinations of progestogen and oestrogen.2 Use of “third” generation progestogens—desogestrel, gestodene, and norgestimate—which had double the risk of thrombosis compared with “second” generation progestogens, sharply declined after warnings of increased risks.
Less than 12 months' use of most hormone replacement formulations increased the risk of breast cancer risk; quantified at 45-63% in the million women study, which also found that current use of hormone replacement doubled the risk of breast cancer and increased breast cancer fatalities by at least 22%. In the million women study and the US Women's Health Initiative (WHI) studies, hormone replacement with progesterone caused four times more breast cancer than with oestrogen only.3,4 Ten years of progesterone or oestrogen trebles the risk of breast cancer compared with five years' use. Hormone replacement therapy increases breast growth and vascularity, making these cancers particularly difficult to diagnose by mammography.
Changes in hormone use have played a large part in changes in the incidence of breast cancer mortality and should not be ignored in studies of the effect of treatments.
Competing interests: None declared.
References
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