Dear Signmecr: Depending on the age of the woman and
her "natural" history, chemotherapy may cause
temporary or permanent menopause. Further, this can
be difficult to define because during perimenopause,
the hormone levels can fluctuate dramatically,
appearing "menopausal" one month and appearing closer
to "normal" at other times. Since it has been three
years and you have been on tamoxifen, you should see a
gynecologist to be certan that this is, in fact,
menstrual bleeding.
One of the risks of Tamoxifen use is an increased chance of developing endometrial cancer. So be certain to follow up on your bleeding, whether or not it is, in fact, menstrual. Not to scare you, but better to be safe. Good luck.