Expression of PDGFRβ in clinical samples. A. Baseline expression of PDGFRβ versus two-week change in the proliferation metagene in 81 breast cancer patients. B. Expression changes of PDGFRβ in response to AI treatment. C. Average percentage change in PDGFRβ expression pre- and post-AI treatment. AI, aromatase inhibitor; PDGFRβ, platelet derived growth factor receptor β.