TTF1 and cancer: The main role for immunohistochemical examination of ATC is to rule out other undifferentiated malignant tumors, such as lymphoma and malignant melanoma.[3] Since the monocyte-like cells in this case showed positive expression of p63 and SATB2 and negative expression of TTF1, TG, PAX-8, metastatic giant cell tumor of bone should be differentiated.