TTF1 and granular cell tumor: ASCO was originally thought to originate from folliculostellate cells (sustentacular-cells in the anterior pituitary gland).[5] Nevertheless, TTF-1 was found to be immune-positive in ASCOs, granular cell tumors, pituicytomas, and normal pituicytes, but negative in folliculostellate cells in the anterior pituitary gland.[6] Mete et al[7] believed ASCOs are a variant of pituicytoma due to the same or similar immunohistochemistry profiles and put forward “oncocytic pituicytoma” for these tumors.