The loss or genetic alterations of several PTPs are shown to promote tumorigenesis, proliferation, and metastasis in in vitro and in vivo models, and these PTPs are generally considered to be tumor suppressors, including PTEN in prostate and breast cancer (28–30), SHP1 in leukemia and lymphomas (31, 32), PTPRF in colon, breast, and lung cancer (33, 34), and DUSP4 in breast, pancreas, and thyroid cancer (35–38). The gene discussed is PTEN; the disease is breast cancer.