I'm pretty sure that's normal. Tamoxifen does not lower estrogen, it blocks estrogen at the receptors. I'm also pretty sure tamoxifen was originally intended as a fertility drug until they realized it causes birth defects. There are studies showing that tamoxifen has estrogenic effects on other tissues because of this. Sorry they are panicking about this!

Tamoxifen is hypoestrogenic (low estrogen) in the breast, but hyper-estrogenic in the uterus and ovaries. So in premenopausal women, it can stimulate the ovaries to produce more estrogen. This can cause benign but sometimes painful cysts on the ovaries. Maybe that is why they have ordered an ultrasound? This effect is also why tamoxifen can stop one’s menstrual periods. I think the body thinks it is pregnant.

You could consider adding ovarian suppression with Lupron.

The ultrasound might show multiple follicles, indicating the ovaries are overstimulated.

Ovarian Cyst Formation in Patients Using Tamoxifen for Breast Cancer

01 October 2005

Abstract

Objective: The purpose of this study was to evaluate patient-related parameters that determine ovarian cyst formation in women using tamoxifen for breast cancer.

Methods: A retrospective review of tamoxifen-treated women with breast cancer who were followed up in the outpatient clinic at Ankara Oncology Hospital between January 2002 and December 2004 was performed. Tamoxifen doses and duration, post-treatment menstrual function, adjuvant therapy, ultrasonographic and hormonal [follicle-stimulating hormone and serum estradiol (E₂)] data, details of gynecologic surgical procedure and histopathology were recorded.

Results: Twenty-nine of 150 tamoxifen-treated patients (19.3%) had ovarian cysts. Cysts were detected in 28 of 57 pre-menopausal women (49.1%) and 1 of 93 post-menopausal women (1.1%). Patients with ovarian cysts had higher serum E₂ levels compared with patients without cysts (24 versus 345 pg/ml; P < 0.001). Patients with ovarian cysts had <1 year amenorrhoea duration (P < 0.001) compared with the patients without cysts. Adjuvant standard chemotherapy did not have relationship between the development of ovarian cysts. Multivariant analysis showed that cyst development is related to high E₂ levels (P < 0.05).

Conclusions: Patients still having a menstrual cycle during tamoxifen had high risk (58.33%) of developing ovarian cysts. We have described an association between pre-menopausal patients using tamoxifen with high E₂ level and ovarian cyst enlargement.