Letters to the Editors

'Tis but a scratch: a critical review of the Women's Health Initiative evidence associating menopausal hormone therapy with the risk of breast cancer

ABSTRACT

Use of menopausal hormone therapy (HT) fell precipitously after 2002, largely as a result of the Women's Health Initiative's report claiming that the combination of conjugated equine estrogen (CEE) and medroxyprogesterone acetate increased breast cancer risk and did not improve quality of life. More recently, Women's Health Initiative (WHI) publications acknowledge HT as the most effective treatment for managing menopausal vasomotor symptoms and report that CEE alone reduces the risk of breast cancer by 23% while reducing breast cancer death by 40%. Their sole remaining concern is a small increase in breast cancer incidence with CEE and medroxyprogesterone acetate (1 per 1,000 women per year) but with no increased risk of breast cancer mortality. This article closely examines evidence that calls even this claim of breast cancer risk into serious question, including the WHI's reporting of nonsignificant results as if they were meaningful, a misinterpretation of its own data, and the misleading assertion that the WHI's findings have reduced the incidence of breast cancer in the United States. A generation of women has been deprived of HT largely as a result of this widely publicized misinterpretation of the data. This article attempts to rectify this misunderstanding, with the goal of helping patients and physicians make informed joint decisions about the use of HT.

Progesterone--promoter or inhibitor of breast cancer

Based on the results of a French cohort of postmenopausal women, it has been claimed that micronized progesterone does not enhance breast cancer risk. The impact of reproductive factors on breast cancer risk and a high prevalence of occult breast carcinomas at the time of menopause suggest an involvement of endogenous progesterone in the development of breast cancer. High mammographic density in the luteal phase and during treatment with estrogen/progestogen combinations reflect a change in the composition of mammary stroma and an increased water accumulation in the extracellular matrix which is caused by hygroscopic hyaluronan-proteoglycan aggregates. Proteoglycans are also involved in the regulation of proliferation, migration, and differentiation of epithelial cells and angiogenesis, and may influence malignant transformation of breast cells and progression of tumors. Reports on a lack of effect of estrogen/progesterone therapy on breast cancer risk may be rooted in a selective prescription to overweight women and/or to the very low progesterone serum levels after oral administration owing to a strong inactivation rate. The contradictory results concerning the proliferative effect of progesterone may be associated with a different local metabolism in normal compared to malignant breast tissue. Similar to other progestogens, hormone replacement therapy with progesterone seems to promote the development of breast cancer, provided that the progesterone serum levels have reached the threshold for endometrial protection.

The World Health Organization defines hormone replacement therapy as carcinogenic: is this plausible?

In June 2005 the World Health Organization's International Agency for Research on Cancer (IARC) classified combined hormone contraception and menopausal therapy as carcinogenic in humans. The IARC's function is to identify potential carcinogens associated with nutrition, environment and pharmaceutical products. They do not produce risk-benefit analyses for any country or population. Their conclusions are highly controversial in that no proof is presented for a causal relationship of estrogens with reproductive cancer, be it plausibility according to mechanisms of action or experimental evidence in an animal model. Equating natural compounds like estradiol with defined carcinogens like asbestos, tobacco smoke as well as indispensable drugs such as aspirin and tamoxifen is of no substantial clinical relevance. Thus, there are no new reasons to change current management principles with combination hormone contraception and therapy.

The effect of medroxyprogesterone acetate on estrogen-dependent risks and benefits--an attempt to interpret the Women's Health Initiative results

The results of the two arms of the Women's Health Initiative (WHI) study allow a comparative assessment of the contribution of the progestogen component to the changes in risk of cardiovascular disease and cancer during treatment of postmenopausal women with conjugated equine estrogens and medroxyprogesterone acetate (CEE/MPA). However, the high proportion of older and overweight or obese women compromises any conclusions, since we estimate that 50% of the women would have the metabolic syndrome. In overweight postmenopausal women with hyperinsulinemia, the risk of breast cancer is elevated and cannot be increased further by hormone replacement therapy (HRT). Therefore, the non-significant, but consistent reduction in breast cancer risk during treatment with CEE alone might be based on an improvement of hyperinsulinemia. The 24% increase in breast cancer risk in the CEE/MPA group can be regarded as an artifact due to very low numbers of breast cancer diagnoses in the placebo group of women who had received HRT prior to the WHI study. The elevated risk of venous thromboembolism and the transient increase in the risk of coronary heart disease (CHD) during treatment with CEE/MPA but not CEE alone suggests a direct effect of MPA on the vessel wall. MPA has been demonstrated to upregulate the thrombin receptor, the thrombin-induced production of tissue factor and procoagulatory activity in the vessel wall owing to its glucocorticoid activity. In contrast, CEE alone reduced non-significantly the risk of CHD in women aged 50-59 years, suggesting that primary prevention is possible if estrogen replacement therapy is initiated early. As clinical studies on the effect of different progestogens combined with estrogens are scarce, a possible superiority of progestogens other than MPA remains to be proven.

Hormone therapy in the WHI era

The announcement in July 2002 in the media of the results of the combined continuous hormone treatment arm of the Women's Health Initiative (WHI) had a profound effect on perceptions about hormone therapy among the lay public and the medical profession. Careful scrutiny of the announcement and the subsequent publications leads to the conclusion that the widespread fear of hormone therapy that was generated was not supported by the facts. WHI was not designed to be, nor can it be, interpreted as a randomised controlled trial of menopausal hormone therapy--rather, it was a trial of chronic disease prevention, particularly aimed at the possible cardiovascular benefits of a specific combination hormone therapy in postmenopausal women. The results, which were consistent with existing data, did not and do not warrant any major change in the previously established guidelines for the use of hormone therapy. Tibolone has emerged as an alternative treatment for menopausal symptoms, but its long-term benefits and risks have yet to be documented.

IARC monographs program on carcinogenicity of combined hormonal contraceptives and menopausal therapy

The World Health Organization International Agency for Research and Cancer (IARC), in June 2005, has classified combination hormone contraception and menopausal therapy as carcinogenic in humans. The IARC's distinction is to identify potential carcinogens associated with nutrition, environment and pharmaceutical products. They do not produce risk-benefit analyses for any country or population. Their conclusions are highly controversial in that no proof is presented for a causal relation of estrogens with reproductive cancer, be it plausibility according to mechanisms of action or experimental evidence in the animal model. Equating natural compounds like estradiol with defined carcinogens like asbestos, tobacco smoke as well as indispensable drugs such as aspirin and tamoxifen is of no substantial clinical relevance. Thus, there are no new reasons to change current management principles with combination hormone contraception and therapy.