CCND1 and cholesteatoma: Since PPAR β/δ promoted cell proliferation of keratinocytes by modulating PTEN/PDK1/ILK/Akt activity [12], consequently, in this study, we hypothesized that the activation of PI3K/Akt/Cyclin D1 signaling mediated by PPAR β/δ may be involved in the abnormal hyperproliferation of keratinocytes in cholesteatoma epithelium.