Uterine effects of tamoxifen: a prospective study

The purpose of the study was to evaluate tamoxifen-associated changes in the vagina and uterus in postmenopausal breast cancer patients. Between June 1994 and December 1998, 45 patients enrolled in a prospective study before commencing tamoxifen therapy. Patients with endometrial thickness >5 mm or neoplasia were excluded. Transvaginal ultrasonography, vaginal maturation indexes (VMI), and endometrial biopsy were performed at baseline and repeated at 6 months (n= 42), 1 year (n= 39), 2 years (n= 32), 3 years (n= 26), 4 years (n= 19), and 5 years (n= 15). For the 39 patients followed for 1 year, VMI (% parabasal/intermediate/superficial) was 21/71/8 at baseline compared with 1/90/9 at 1 year (P value = 0.0008/0.001/0.78). At baseline, mean endometrial thickness and uterine volume were 2.6 mm and 64 cm(3), respectively, compared with 5.8 mm and 84 cm(3) at 1 year (P= 0.0002, 0.002). At baseline, 80% of patients had atrophic endometrium and 9% proliferative endometrium compared with 61% and 26% at 1 year, respectively (P= 0.04). No cases of endometrial hyperplasia or adenocarcinoma were detected. Findings observed at 6 months persisted through 5 years of follow-up. Tamoxifen exerts a weak estrogenic effect on the vagina and uterus in highly prescreened postmenopausal women without preexisting endometrial pathology.