Advances in endocrine treatments for postmenopausal women with metastatic and early breast cancer

Aromatase inhibitors in advanced breast cancer

The third-generation aromatase inhibitors suppress whole-body estrogen production in postmenopausal women with high specificity and potency. In women with hormone-sensitive breast cancer, three of these agents, letrozole, anastrozole, and exemestane, provide an important alternative endocrine therapy to the antiestrogen tamoxifen, which blocks estrogen activation of the estrogen receptor. For treatment of advanced or metastatic breast cancer that has progressed on first-line tamoxifen, all three agents are active. On that basis, they have each been compared with tamoxifen as first-line therapy of advanced breast cancer, in phase III trials. Letrozole was significantly superior to tamoxifen in the primary end point, median time to progression, as well as in response rate and clinical benefit rate, and treatment was well tolerated. Although there was no significant difference in median overall survival, an advantage seen with letrozole for the first 2 years may have been lost because of crossover to the alternate agent at disease progression. Anastrozole was evaluated in two separate trials designed for combined analysis. Overall, anastrozole was at least equivalent to tamoxifen in activity, but clearly superior only for median time to progression in the subgroup of patients with hormone receptor-positive disease. Treatment was generally as well tolerated as tamoxifen. In an early report, exemestane was significantly better than tamoxifen in response rate and median time to progression, with overall survival data not yet available. To date, letrozole appears to be the most effective aromatase inhibitor in the first-line advanced breast cancer setting.

Arimidex inhibition on proliferation of human breast solid tumors measured by ATP bioluminescence

To determine the degree of Arimidex (Anastrozole) inhibition on proliferation of human breast solid tumors in vitro by ATP bioluminescence assay. Breast cancer solid tumors with different hormone receptors and grading were collected from 38 Chinese women with invasive breast cancers. Tumors were treated with three concentrations of Arimidex (1.5 mM, 15 mM and 150 mM). ATP bioluminescence assay was used to measure the metabolic rate in order to determine the degree of inhibition of Arimidex on the breast cancer tumors by comparing to the untreated tumors. 15 mM Arimidex shows greatest inhibitory effect on the proliferation of solid tumors with ER-postive/PR-positive. It can also inhibit the growth of metastatic tumors and tumors with HER-2/neu expression. It shows greater inhibitory effect in lower grading of tumors then higher. Arimidex may effectively inhibit the growth of breast tumors in in vitro system by inhibiting aromatase and block estrogen dependent tumor growth.

Effects of the Antiestrogen Tamoxifen and the Aromatase Inhibitor Letrozole on Serum Hormones and Bone Characteristics in a Preclinical Tumor Model for Breast Cancer

PURPOSE

The purpose of this study was to evaluate and compare the effects of the antiestrogen tamoxifen and the aromatase inhibitor letrozole on tumor growth, serum hormones, uterine weight, body composition, and bone characteristics in mice.

EXPERIMENTAL DESIGN

Human estrogen-dependent breast cancer cells stably transfected with the aromatase gene (MCF-7CA cells) were inoculated in Matrigel subcutaneously into ovariectomized nude mice. This model represents postmenopausal breast cancer in many respects, including the fact that estrogen is no longer produced by the ovaries and is not under feedback regulation by gonadotropins. Mice that received subcutaneously implanted MCF-7CA cancer cells were then treated with tamoxifen or letrozole for 7 weeks.

RESULTS

As reported previously, tumor growth was markedly inhibited by both tamoxifen (100 microg/day) and letrozole (10 microg/day). Tamoxifen treatment led to increased bone mineral density (BMD) and hyperplastic uteri. Mice treated with letrozole had significantly smaller uteri than the controls and tamoxifen-treated mice. Letrozole did not affect BMD. There was no significant difference in systemic leptin and insulin-like growth factor I levels as a result of tamoxifen or letrozole treatment.

CONCLUSIONS

Tamoxifen treatment inhibited breast cancer cell growth and increased BMD but caused uterine hypertrophy in this preclinical model of postmenopausal breast cancer. Letrozole inhibited tumor growth without inducing uterine hypertrophy. In addition, letrozole had no effect on BMD. These findings provide experimental evidence that letrozole is an effective and safe (in terms of risk of endometrial cancer risk and osteoporosis) alternative or complement to tamoxifen treatment for breast cancer.