Does HRT modify risk of gynecological cancers?

A substantial body of recent experimental, clinical and epidemiological evidence indicates that hormones play a major role in the etiology of several human cancers. The ability of hormones to stimulate cell division in certain target organs such as the breast, endometrium, prostate and the ovary, may lead following repeated cell divisions to accumulation of random genetic errors that ultimately produce the neoplastic phenotype. Hormone-related cancers account for more than 30% of all newly diagnosed female cancers in the United States. While most non-hormone-dependent adult cancers rise continuously with age, hormone-responsive cancers of the breast, the ovary and the endometrium rise with age until menopause, and then distinctly level off to a plateau. These epidemiologic characteristics may indicate that the key etiologic events for these cancers occur in the premenopausal period. Prevention strategies that intervene during the premenopausal period can be expected to have a greater long-term impact in reducing risk than those implemented for an equivalent length of time in the postmenopausal years. Epidemiological studies demonstrate a reduction in endometrial cancer risk of about 11.7% per year of combination oral contraceptive (COC) use; ovarian cancer risk may be reduced by 7.5% per year of COC use, while breast cancer studies have produced mixed results. A comparison of age-adjusted incidence and mortality rates for women less than 50 years of age between the years 1973-1974 and 1986-1987 demonstrate a change in the average rate of breast cancer of plus 9.6% incidence and minus 8.2% mortality; the rates reflect the cancer burden of women who would and would not have had access to COCs during the majority of their child-bearing years. The use of hormone replacement therapy (HRT) is well established to provide short-term relief of symptoms related to menopause and long-term protection from the consequences of estrogen deficiency, such as postmenopausal osteoporosis and cardiovascular disease. Besides COCs, use of HRT constitutes the other major setting in which exogenous steroid hormones are widely used in essentially healthy women and has had a remarkable impact on cancer incidence and mortality. Estrogen replacement therapy (ERT) and endometrial cancer risk are strongly associated with respect to both dose and duration. Endometrial cell mitotic activity during continuous high-dose estrogen monotherapy equals that observed during the follicular phase of the menstrual cycle, and the total mitotic activity over a 28-day period amounts to roughly double that of a premenopausal woman as long as there is no opposition by a progestogen.(ABSTRACT TRUNCATED AT 400 WORDS)