Breast Cancer Higher in Women on HRT

Dr. Heward shares why we see more breast cancer when we study women on HRT.

Why Do We See Increased Incidences Of Breast Cancer When We Study Women On Hormone Replacement Therapy/HRT? When we do a study where we compare women on estrogen with women who don’t go on estrogen, we report that the women who got estrogen got more breast cancer and the conclusion or the implication is that somehow estrogen caused that breast cancer. But there are no data to my knowledge and remember I am a molecular endocrinologist so I study how hormones work at the molecular level and there are no data anywhere I know of that indicate that estrogen has the ability to take a normal, healthy breast cell and change it to a cancer cell. That does not happen. So, how then can we explain the increased incidents of breast cancer in women on estrogen replacement therapy and the answer is, what we do know about estrogen is that it’s atrophic hormone which means it stimulates growth in some of the tissues in which it has receptors, like the breasts. So, if I took estrogen, my breasts would grow. In a woman who has an estrogen-sensitive breast cancer, estrogen may actually stimulate the rate of growth in the cancer itself, so during the time frame of the study, are you more likely to pick up a fast-growing cancer or a slow-growing cancer? What’s probably going on is there’s no more breast cancer in the estrogen group than there is in the control group but just more diagnosed breast cancer because the tumors are growing faster.