Three patients developed breast cancer within 3-6 months of starting progesterone cream.

Hi Catherine,

I just spoke to a friend today who is a ob/gyn nurse. She said they have had 3 patients who had started on natural progesterone cream develop breast cancer within 3-6 months of starting the cream. What could have caused it? I thought the progesterone cream was supposed to decrease your risk for breast cancer. Please answer if you can because this information has me really concerned about my using the cream. Thank you.

Thank you,

Angi

Dear Angi,

If these three women developed breast cancer within 3-6 months of starting topical progesterone cream the cancers were already present and the progesterone may not have been sufficient to stop a runaway train (cancer).

It would be of interest to know what type of breast cancers these were (insitu or invasive), how fast they were growing (mitotic index or MiB1 (Ki67), and if they contained estrogen and progesterone receptors.

In cancer cells that contain progesterone receptors, progesterone should slow the growth of cancer and push it towards a more differentiated state. This progesterone-induced differentiation requires cell division so it is possible that progesterone was allowing the cancer cells to proliferate and differentiate (specialize) simultaneously.

On the other hand it is possible that the breast cancer cells did not contain progesterone receptors, which would prevent them from responding to the anti-estrogenic actions of progesterone (ie, progesterone down-regulates estrogen receptors and desensitizes tissues to further growth-promoting actions of estrogens).

A third possibility is that the progesterone cream was of insufficient strength to have full anti-estrogenic effects. Low dose progesterone works in synergy with estradiol to stimulate growth and proliferation. I would question what the estradiol and progesterone levels were in these women who developed breast cancer while taking progesterone.

Most oncologists and general practioners that work with natural progesterone find that primary breast cancer, and breast cancer recurrences are less frequent in women using topical progesterone, but it does happen. My experience, in reviewing pathology reports from women who have developed breast cancer while using topical progesterone, is that they usually have tumors that do not contain progesterone receptors, or the receptors are very low.

When someone claims they know of women who have used progesterone and then developed breast cancer you should get more detailed information. We could then share this with the group and I would be glad to give you my interpretation from a scientist’s point of view.

Best regards

Dr Zava