periods and tamaxifen

I am a 46 y.o. female w/ stage 1 breast cancer insitu.  I received 7 weeks of radiation and am now on tamaxifen.  Is it unusual to have a prolonged period (13 days and hasn't stopped )while you are on this drug?  I have been on this for 3 months.  Thanks.

[CCF-RN,MSN-rf]

Dear Qball:  Tamoxifen is a SERM (selective estrogen receptor modulator) drug. This means that in some organs (the breast) estrogen is blocked. In other organs, such as the uterus, estrogen levels are actually higher. This helps to explain why the incidence of uterine cancer in women taking tamoxifen is higher. Although, many women do develop amenorrhea (absence of menstrual period), it is not uncommon for premenopausal women to have periods. It is also technically possible for a woman to become pregnant while taking tamoxifen, although this is certainly not recommended. Since you have just begun tamoxifen, it is difficult to sort out what the prolonged bleeding might mean.  However, if you have not had a pelvic exam and PAP test recently, you should proceed with doing so.