Objectives: We aimed to determine the safety and efficacy of anastrozole in PAH.

Larger and longer phase II clinical trials of anastrozole may be warranted in patients with PAH.

Here we report a pharmacokinetic subset analysis investigating a possible drug interaction between anastrozole and fulvestrant.

None of the three biomarkers identified a set of patients with differential benefit from anastrozole over tamoxifen.

Methods: Post-menopausal patients with HR-positive metastatic breast cancer were randomized to anastrozole with or without concurrent fulvestrant.