Role of hormones in cancer prevention.

Risk for breast cancer can be easily and rapidly assessed using validated, quantitative models. Multiple randomized studies show that the selective estrogen response modifiers (SERMs) tamoxifen and raloxifene can safely reduce the risk of invasive breast cancer in both pre- and postmenopausal women. Treatment resulted in a 38% reduction in breast cancer incidence, and 42 women would need to be treated to prevent one breast cancer event in the first 10 years of follow-up. Reduction was larger in the first 5 years of follow-up than in years 5 to 10, but no studies treated patients for longer than 5 years. Thromboembolic events were significantly increased with all SERMs, whereas vertebral fractures were reduced. Tamoxifen provides net benefit to all premenopausal women who are at increased risk, whereas raloxifene reduces risk nearly as much in postmenopausal women and offers increased safety. Both tamoxifen and raloxifene reduce the incidence of in situ cancers. Lasofoxifene reduced the risk of breast cancer by 79% in postmenopausal women with osteoporosis. The MAP3 trial showed a 65% reduction in the annual incidence of invasive breast cancer in postmenopausal women who were at moderately increased risk for breast cancer who took the aromatase inhibitor exemestane. The IBIS-II trial showed a 53% reduction in the risk of invasive breast cancer in postmenopausal women aged 40 to 70 who took the aromatase inhibitor anastrozole. Of the 50 million white women in the United States aged 35 to 79, 2.4 million would have a positive benefit/risk index for chemoprevention.

Mechanisms in progestin antagonism of pituitary tumorigenesis.

Chronic exposure of F344 rats to diethylstilbestrol (DES) induces pituitary tumors (DES-T) composed of proliferating lactotrophs. Presently, we studied the effect of progestins on parameters related to tumor growth and function, due to previous evidences of progesterone antagonism of pituitary tumorigenesis acting at pituitary and hypothalamic levels [Piroli, G., Grillo, C., Ferrini, M., Lux-Lantos, V. and De Nicola, A. F., Antagonism by progesterone of diethylstilbestrol-induced pituitary tumorigenesis in Fischer 344 rats: Effects on sex steroid receptors and tyrosine hydroxylase mRNA, Neuroendocrinology, 1996, 63, 530-539]. In search of a quantitatively more important effect, animals bearing DES-T were treated with synthetic progestins. Competition assays using DES-T as source of progestin receptors indicated that levonorgestrel (LNG), gestodene and R5020 showed higher affinities (IC50 1-2 nM) than progesterone, norethisterone and medroxyprogesterone (IC50 10-25 nM). Treatment with LNG reduced DES-T weight by 45%, and serum PRL by one half. Small (monomeric) and big (polymeric) PRL increased 5- and 2.5-fold, respectively, in DES-T in comparison with pituitaries of ovariectomized (OVX) rats. However, LNG produced no changes indicating that synthesis and storage of PRL was conserved in rats receiving both hormonal treatments. DES induced a 15-fold increase in cell proliferation, measured as bromodeoxyuridine incorporation into cell nuclei, in comparison to OVX rats, while LNG treatment of DES-T bearing rats reduced this index by 72%. Electron microscopic images showed that LNG markedly reduced hypertrophy and hyperplasia of lactotropes, increasing the proportions of degenerating cells and cells of high electronic density with alterations of cytoplasmic organelles. However, histopathological signs of apoptosis were absent. Therefore, reduced cell proliferation and non-apoptotic cell death are part of the mechanisms employed by progestins to antagonize tumorigenesis at the pituitary level. The results may open a new therapeutic strategy for treatment of PRL secreting adenoma in humans.