PKM and nasopharyngeal carcinoma: However, in thyroid malignancies, IRF5 promotes cancer cell proliferation.259 IRF6, as a tumor suppressor gene and transcription factor, functions to suppress tumorigenesis in nasopharyngeal carcinoma (NPC), squamous cell carcinomas (SCCs),and renal clear cell carcinoma.260–262 In glioma, IRF6 impaired cell proliferation and induced apoptosis by inhibiting pyruvate kinase isozyme type M2 (PKM2) and glucose transporters 1 (GLUT1) transcription.263 The regulation of tumor development by IRF family members will be extensively reviewed in later chapters.