Breast cancer risks with hormone replacement therapy

This study evaluated breast cancer risk and outcomes among postmenopausal women using hormone replacement therapy.

Progesterone and estrogen are steroid hormones that have a crucial role in female maturation and reproduction processes. The female menstrual cycle, ovulation and pregnancy are only part of the processes in which these hormones take part.
During and after menopause, progesterone and estrogen levels sharply decline leading to a series of symptoms such as rapid heartbeat, hot flashes, depression, skin and vaginal dryness, muscle pain and urgency of urination. Hormone replacement therapy employs estrogen and progestin (a synthetic progesterone) to relieve menopausal symptoms.

Though having many advantages, hormone replacement therapy has been suggested to increase the risk of developing breast cancer. Since breast cancers are often dependent on progesterone and estrogen for growth and spread, previous use of hormone replacement therapy may also influence cancer progression and treatment outcomes. However, the correlation between previous hormone replacement therapy and breast cancer remains poorly understood.

41,449 postmenopausal women were followed in this study. 25,328 women were not receiving hormone replacement therapy (non-hormone users) and 16,121 were receiving hormone replacement therapy (estrogen plus progestin users). During an average follow-up of 11.3 years, 2,236 invasive breast cancers were diagnosed. Indeed, the incidence of breast cancer among hormone replacement users was higher (0.6%) compared to non-users (0.42%). Further analysis indicated that women initiating hormone replacement therapy closer to the time of menopause (defined as last menstrual bleeding) were at a higher risk than women initiating replacement therapy years later.

An analysis of prognosis and survival after diagnosis of breast cancer revealed no significant differences between women diagnosed after receiving hormone replacement therapy and women never receiving hormone replacement therapy.

This study concluded that postmenopausal estrogen and progestin use is associated with increased breast cancer incidence, although cancer prognosis seems to be unaffected by previous hormone replacement therapy.