FOXO1 and neoplasm: FOXO is a transcription factor that functions as a tumor suppressor. FOXO triggers cell cycle arrest and apoptosis after it enters the nucleus. Phosphorylation of FOXO (pFOXO) causes export from the nucleus and inactivates its tumor suppressor function. Trastuzumab inhibits HER2+ cells by reactivation of FOXO1A [15]