Evidence is piling up for the fact that breast cancer incidence is increased in current users of menopausal hormone therapy. A large prospective study in the United Kingdom that investigated the effect of the timing of hormonal therapies on breast cancer incidence has given fresh insight into the problem. Starting hormone therapy at around the time of menopause was found to be associated with a very high risk of breast cancer.
The conclusion indicates that a longer gap between the institution of therapy and menopause would be better. The Journal of the National Cancer Institute reported that '
starting hormone therapy five years or more after menopause had little or no increased risk, regardless of the type of hormone therapy used, how long they used it, and whether they were overweight or not'.
Menopausal hormones are recommended to counter some of the problems often associated with the onset of menopause, i.e. the time when menstruation ends. It usually involves treatment with the two female hormones, estrogen and progesterone: either estrogen alone or estrogen in combination with progesterone or progestin. Progestin is a synthetic hormone with effects similar to those of progesterone. The use of estrogen - progestin is associated with a greater incidence of breast cancer when compared to that of estrogen-only formulations. Daily use of combined HRT is known to increase a woman's chance of developing breast cancer by about 5% to 6% of the non-hormone risk with each year of use. Estrogen only therapy is safer. The timing of therapy was however always a matter of confusion.
Previous studies had suggested that the interval between menopause and initiating hormone therapy would influence breast cancer risk. Data from the Million Women Study (MWS) that included 1.13 million women were analysed. Researchers also compared women on different types of hormone therapy. The study revealed that breast cancer incidence was increased in current users of hormonal therapy, returning to that of never users a few years after use had ceased.
The carcinogenic potential of menopausal hormone therapy was found to be unaffected by factors like body mass index, the age at menarche, height, and having a ﬁrst-degree relative with breast cancer. 'In this large prospective study, we found substantial and clinically important heterogenecity in the effects of hormonal therapy on breast cancer incidence among postmenopausal women', claims the authors.
Reference: Journal of the National Cancer Institute