Hormonal Therapy: Current Status in the Treatment of Metastatic Breast Cancer

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Introduction

In general, metastatic breast cancer (MBC) is treated systemically using chemotherapy, hormonal therapy, and newer targeted therapies when appropriate. About 75% of breast cancers test positive for estrogen receptors (ER) and progesterone receptors (PR), and estrogen stimulation of these receptors plays an important role in the proliferation of these tumors.¹

For patients with ER/PR-positive breast cancer, hormonal therapy is the preferred treatment if possible. For patients with rapidly progressive tumors or those in visceral crises, chemotherapy may be preferred because of its rapid rate of response, although even in this situation, hormonal therapy may be feasible.

Hormonal therapy is generally attractive because there are a variety of effective options available and the toxicities are generally mild. An important indicator of response is the presence of the ER and PR on the tumors² and their quantitative levels.³ Following the observation by Sir Beatson over a century ago that oophorectomy in premenopausal women induced tumor regression,⁴ hormonal therapy has been extensively used in the treatment of patients with ER/PR-positive breast cancer. The mechanisms of action of hormonal agents include:

• blocking the interaction between estrogen and estrogen receptors with selective estrogen receptor modulators (SERM);
• degrading the estrogen receptors with selective estrogen receptor down-regulators (SERD); and
• inhibiting estrogen production with an aromatase inhibitor (AI) or with surgical, radiation, or chemical ovarian ablation in premenopausal patients.

This E-Update will focus on the hormonal treatment options for MBC.