This study is a phase I, single arm, open-label trial of PD0332991 in combination with
Paclitaxel in patients with Rb-expressing metastatic breast cancer. Up to 20 patients are
anticipated to be enrolled to reach the Maximum Tolerated Dose (MTD) of PD0332991 in
combination with Paclitaxel. Once the MTD is established, an additional expanded cohort of 10
patients will be enrolled at that dose to establish the Recommended Phase 2 Dose (RP2D),
obtain additional safety data and perform exploratory biomarker studies.