KDR and neoplasm: Several studies have shown that PTPN2, which exerts tumor suppressive effects in skin carcinogenesis, suppresses proliferation and induces apoptosis by negatively regulating multiple oncogenic signaling pathways, including STAT1, STAT3, STAT5, PI3K/AKT, and fetal liver kinase 1 (Flk-1)/JNK signaling pathways (137–139).