Recent studies confirm previous findings that estrogen-alone therapy may actually reduce the incidence of breast cancer in certain women. Theses finding seems confusing because estrogen is recognized to stimulate breast cancer growth in some patients.
The confusion stems for previous findings of the Women’s Health Initiative, when their trial of combination estrogen plus progesterone was stopped in July 2002 because of an increase risk of breast cancer and stroke. Two years later, the Estrogen-Alone segment was stopped.
Evaluation of the Women’s Health Initiative data looking at Estrogen-Alone use in postmenopausal women with prior hysterectomy found breast cancer was reduced in women who were receiving estrogen therapy alone compared to those that were not using estrogen.
It appears that Long-Term Estrogen Deprivation may be the Key. Dr. Jordan, considered the father of tamoxifen therapy explains: “We know that if breast cancer cells are deprived of estrogen, the majority of the cells die off, and then cells come back that can grow with a minimum of estrogen. The same is true for when we treat with antihormone therapy,” he continued. “The cells stop growing, and after a long time become resistant. What we know is, if you put estrogen back after you stop the therapy, the cells die. The estrogen kills the cells.”
The onset of menopause “switches” off the ovary and starves the breast of hormones, and in turn, the lack of circulating estrogen now produces an estrogen-withdrawal-like effect. “So the occult breast cancer cells that are already in the breast now start to learn to grow very slowly, with very little available estrogen,” said Dr. Jordan. “When the woman then uses estrogen replacement therapy, say at about age 60 or older, it does the exactly the same as we see with the cells in the laboratory — it causes those microcells in the breast to die off.
“And that is why we saw fewer breast cancers in that trial,” he noted.
The findings suggest that women that have been off estrogen for sometime may benefit from the addition of estrogen in the prevention of breast cancer. Further studies are needed.
J. Kyle Mathews, MD
Plano OBGyn Associates
Plano Urogynecology Associates