Methods for the use of Pin1 as a marker of abnormal cell growth are disclosed. In one embodiment, the method includes detecting a level of Pin1 to stage an abnormal cell growth, such as breast or prostate cancer. In another embodiment, the method includes evaluating the efficacy of a treatment of an abnormal cell growth, such as cancer, by monitoring the levels of Pin1. In another embodiment, the method includes evaluating the extent of metastasis of abnormal cell growth, such as cancer. The levels of Pin1 can be protein levels or nucleic acid levels.