Dr. Haddad on the Effect of Anastrozole on Endocrine Suppression in ER+/HER2- Breast Cancer

Tufia C. Haddad, MD, medical oncologist, associate professor of oncology, Mayo Clinic Comprehensive Cancer Center, discusses key results from a prospective trial on adjuvant anastrozole in estrogen receptor (ER)–positive, HER2-negative breast cancer.

Matched case-control studies from several previous trials utilizing an aromatase inhibitor (AI) have indicated that an inadequate degree of estrogen suppression induced by AI correlates with a higher risk of breast cancer recurrence events. Therefore, a prospective trial was designed to explore this potential connection by investigating the effect of the AI anastrozole on estrone and estradiol levels in postmenopausal patients with stage I to III ER-positive, HER2-negative breast cancer. Moreover, the trial assessed the safety and pharmacodynamics of anastrozole in evaluable patients who experienced inadequate estrogen suppression. Patients included in the trial were eligible for treatment with an AI after previously completing locoregional therapy and chemotherapy.

Results demonstrated that 29% of postmenopausal patients receiving a standard 1 mg daily dose of adjuvant anastrozole exhibited inadequate endocrine suppression, Haddad says. Of these 41 patients, 32 initially remained on treatment and continued to receive anastrozole at an increased dose level of 10 mg, followed by treatment with letrazole