Abstract Bladder cancer (BC) is a current clinical and social problem. At diagnosis, 70% of the patients display non-muscle invasive tumor (NMIBC), a relatively indolent disease treated by transurethral resection followed by local instillation in some cases. Unfortunately, NMIBC displays an extremely high recurrence rate, and these recurrent tumors may display tumor progression showing muscle invasive (MIBC) characteristics. MIBC is treated, in most cases, by cystectomy and platinum-based chemotherapy. Nonetheless, the metastatic spreading occurs very often with fatal consequences. Various targeted therapies are being clinically and preclinically tested for BC management. Palbociclib (PD-0332991) is a cdk4/6 inhibitor currently tested for the treatment of other malignancies characterized by the presence of a functional RB1 gene. Since RB1 mutation occurs in only 20-30% of BC, we hypothesized the potential use of Palbociclib for BC management. A series of BC cell lines of known genomic characteristics and differing in their RB1 status, were tested for their sensitivity to Palbociclib. Unexpectedly, we observed a similar response to Palbociclib in pRb wt and pRb mutant cell lines in vitro and in xenografts in vivo, although with different biochemical and cell cycle effects. Genomic characterization of these treated cells shows strong gene expression divergence as a consequence of Palbociclib treatment in pRb wt and mutant cells. Nonetheless, bioinformatic analyses revealed FoxM1 as a possible common regulator of some downregulated genes in both cases. Importantly, FoxM1 has been demonstrated a bona fide cdk4 substrate and may confer cis-platinum resistance. We observed reduced FoxM1 phosphorylation upon Palbociclib treatment in all cell lines tested, and also increased sensitivity to cis-platinum. Remarkably, we found that phosphorylated FoxM1 is a potential poor prognosis factor in human NMIBC clinical samples. Future studies, using various NMBIC and metastatic MIBC transgenic mouse models based on the genetic inactivation of Rb1 with other tumor suppressor genes, will precede the possible development of appropriate clinical trials testing the use of Palbociclib in the management of BC patients. This abstract is also being presented as Poster A04. Citation Format: Carolina Rubio, Fernando López-Calderón, Cristina Segovia, Marta Dueñas, Mónica Martínez-Fernández, Irene Otero, Federico de la Rosa, Felipe Villacampa, Daniel Castellano, Jesús M. Paramio. Therapeutic targeting of cdk4 in bladder cancer. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr PR01.