Overexpression of cyclin‐dependent kinase 4 protein in extramammary Paget's disease

Cyclin‐dependent kinase 4 and 6 (CDK4/6) plays an important role in cell cycle progression, and the CDK4/6–cyclin D1 complex controls the cell cycle transition from G1 phase to S phase. CDK4 is enhanced in several types of cancers and CDK4/6 inhibitors attenuate the proliferation of several types of cancer in vitro/in vivo. The purpose of our study was to investigate the expression pattern of CDK4 and evaluate its clinical importance in extramammary Paget's disease (EMPD). Almost all EMPD tissues were positive for CDK4, and metastatic lesions had a similar immunostaining intensity to primary lesions. In addition, CDK4 protein levels were positively correlated with those of cyclin D1 protein. Taken together, CDK4 may assume a crucial role in EMPD progression.