Effect of a half dose of tamoxifen on proliferative activity in normal breast tissue

To investigate the proliferative activity of the mammary gland epithelium and plasma levels of progesterone, estradiol, prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and sex hormone-binding globulin (SHBG) in premenopausal women treated with 10 and 20 mg of tamoxifen (TAM) for 22 days.

A randomized double-blind study was performed with 43 premenopausal women with a diagnosis of fibroadenoma of the breast. The patients were divided into three groups: A (n = 15, placebo); B (n = 15, TAM 10 mg/day) and C (n = 13, TAM 20 mg/day). They started taking an oral dose of TAM or placebo on the very first day of the menstrual cycle. Lumpectomy was performed on the 22nd day of therapy. Normal breast tissue samples were collected during surgery, immediately immersed in 10% buffered formalin, processed for routine histology and immunohistochemistry for proliferating cell nuclear antigen (PCNA) detection. Two peripheral blood samples were collected, both on the 22nd day of the menstrual cycle, in order to evaluate the hormone levels. PCNA expressing epithelial cells were quantified by using a digital program Kontron Image System KS-300 in 1000 cells (400 x ).

The percentage of cells expressing PCNA was significantly higher in the group receiving placebo (group A, 50.3%) when compared to groups receiving TAM 10 or 20 mg/day (group B, 24.1%; and group C, 23.2%, respectively) (P < 0.001). Differences between groups B and C were not significant. Levels of progesterone, estradiol and SHBG were significantly higher in B and C groups compared to group A. Increasing concentrations of FSH (P < 0.0045) and lower levels of prolactin (P < 0.0055) were only found in the group receiving 20 mg/day of TAM (group C).

A 22-day TAM therapy, either with 10 or 20 mg/day, significantly reduced the PCNA expression and therefore the proliferative activity of the normal human breast tissue. Increasing levels of estradiol, progesterone and SHBG were associated with TAM therapy at 10 or 20 mg/day. However, a significant change of the level of FSH and prolactin was reached only with a 20-mg/day dose.