Breast Cancer Risk Study Evaluation

(Excerpt from letter by Patricia T.Kelly, Ph.D. to a breast cancer patient having her risks assessed)

Long term studies generally find no significant increase in breast cancer risk to HRT users when estrogen dose is increased or when estrogen is taken for up to 20 years. Women who have a family history of breast cancer or a personal history of benign breast disease and who take replacement hormones are not at increased risk of breast cancer compared to non-users with similar risk factors.

In studies reporting a statistically significant increase in breast cancer risk to HRT users, the actual or absolute increase is quite small and the duration of use differs in the various studies, suggesting that the increases could be due to chance fluctuations or study design. An international group that assessed most studies published before 1997 estimated that an additional 0.3 breast cancer would be found in 100 women who used HRT for ten years. A more recent study concluded that ten years of estrogen only use would result in an additional 0.5 breast cancer in 100 women in 15 years. Use of both estrogen and progesterone would result in 1.9 additional breast cancers in 100 women in the course of 15 years. These increases are so small that they may well be due to chance, to better health practices in HRT users, or to subtle differences between the study groups.

Many studies, including the prestigious Nurses Study, find that women who take HRT are not at increased risk of death due to breast cancer. In fact, most studies find that HRT users have an improved overall survival compared to nonusers.

The Women's Health Initiative study found that women who took Prempro, a particular type of HRT, had a very small increase in breast cancer risk—eight hundredths of one percent a year. Even this small difference may not be due to the hormone use, since the average follow-up was only about five years. Breast cancers are estimated to take from seven to ten years to be detected, so all or most of the breast cancers found during the study were probably present before the study and so before the Prempro use began. The average age of the women in this study was 63, so the results do not apply to women who start using HRT at menopause.

More than 15 studies now find that women who were taking estrogen at the time of their breast cancer diagnosis have a prognosis as good or better than that of women who were not taking hormones when they were diagnosed. In these studies the breast cancers found in women taking HRT tended to be smaller, slower growing, and less aggressive than those in non-users.

In over 30 studies, women taking replacement hormones after a breast cancer diagnosis have as good or a better prognosis than non-users. One recent study compared prognoses in 174 women who took HRT after a breast cancer diagnosis with that of 695 matched non-users.

In this study, HRT use for 13 or more months was not associated with a significantly greater recurrence rate. Similarly, women who took higher doses of estrogen had recurrence rates that did not differ significantly from those who took lower doses or no hormones. As a group, users of HRT were half as likely as non-users to have a recurrence, up to 4.6 years. Oral HRT users had a breast cancer mortality rate of 0.2 compared to non-users. These differences were statistically significant.

Another study compared 15 year survival in 125 women who used HRT after breast cancer with that of 362 who did not. Users had a survival of 88% compared to 63% for non-users. Interestingly, in this study 30% of the users were stage II or higher.

Far more women over age 50 die of cerebrovascular and heart disease than of breast cancer. A number of studies find that women who start HRT at menopause have half the chance of dying of heart and cerebrovascular disease compared to non-users.