TTF1 and neoplasm with perivascular epithelioid cell differentiation: Postoperative pathological findings: left lobe thyroid: malignant perivascular epithelioid cell tumor (PEComa) Components: immunohistochemistry showed Vimentin (partially +), Smooth muscle actin (SMA) (+), Desmin (+), HMB45 (small foci +), P53 (missense mutation +), and Ki-67 (about 50% +); Follicular carcinoma component: immunohistochemistry showed cytokeratin (CK) (+), PAX8 (+), thyroid transcription factor 1 (TTF1) (+), thyroid peroxidase (TPO) (+), P53 (wild-type +), and Ki-67 (approximately 3%+) (Figures 2A–L).