Targeting the PAM50 Her2-Enriched Phenotype With Enzalutamide in Hormone Receptor-Positive/Her2-Negative Metastatic BC

A strong rationale accumulated over the years suggests that within HR+/HER2-negative breast cancer, tumors falling into the PAM50 HER2-enriched subtype have androgen receptor (AR)-dependency. To test this hypothesis directly in patients' tumors, we propose an exploratory, open-label, non-randomized, two-cohort, multicenter, prospective, phase II study which evaluates the effect of enzalutamide on proliferation after 2 weeks (14-21 days) of treatment in patients with endocrine-resistant, locally advanced or metastatic HR+/HER2-negative breast cancer. After 2 weeks (14-21 days) of treatment, patients will continue enzalutamide. Exemestane will be allowed to be added to enzalutamide per investigator discretion and will be administered until progression or unacceptable toxicity.