 This multicenter phase II trial will evaluate palbociclib PD-0332991 in patients with metastatic urothelial carcinoma UC with cyclin-dependent kinase inhibitor 2A CDKN2A also referred to as p16 loss and positive Retinoblastoma Rb expression after failure of first-line chemotherapy. The study will enroll up to 40 patients to identify 36 evaluable patients, using a Simons two-stage design, with a primary endpoint of progression free survival PFS at 4 months PFS4. Secondary objectives include estimating median PFS, overall survival OS, response rate RR and exploratory objectives include an evaluation of molecular predictors of response and resistance. 