I would call your oncologist and let the doc know and make an appointment with your GYN. Tamoxifen has a 7% chance of causing uterine cancer.

I am 51 and my periods on Tamoxifen have been regular except for when I am under extreme stress (before my surgeries they stop for a couple of weeks but resume once life returns to normal, but this was the case before Tamoxifen also)
My oncologist defers all gyn issues to my gyn who is very well informed about BC issues so I would call my gyn.
Since being on Tamoxifen I have had cramping, sometimes a couple of days before my period starts, and my periods became very heavy. They have since returned to normal after my D&C.

Tamoxifen DOES NOT cause menopause! @A MyBCTeam Member tamoxifen does not stop a woman from ovulating, in fact women CAN get pregnant on Tamoxifen. It is only designed to block hormone receptors. You're still producing estrogen and so spotting or having periods is perfectly normal if you've been deemed pre-menopausal. Only blood tests can determine that. Also, if you've been through chemo prior to starting Tamoxifen it most definitely messes with your ovarian function - my periods stopped completely for 16 months with chemo but they returned normal and I was age 46. You should notify oncologist but I've known many women who had their periods all throughout Tamoxifen. The only drugs that stop estrogen production (from other glands, not ovaries) are aroma taste inhibitors and those are only prescribed to post menopausal women. Understanding what Tamoxifen does and doesn't do and how it functions will clear up this confusion.

Mentioned Users

A MyBCTea...

@A MyBCTeam Member - Don't feel foolish. More now than ever you need to listen to your body and insticts. The waiting is the worst. You'll be fine.

Mentioned Users

A MyBCTea...

Saw the OB/GYN today. She thinks this is a "last hurrah" period, especially since there was cramping involved, but did a biopsy just to check. I should get the results back sometime this week or next. I asked if I should call if it happens again and she said that it would depend on the biopsy results. Sigh. I always feel foolish when a symptom turns out to be nothing but I sure don't want it to be something!