Sections show a low-grade cellular spindle cell neoplasm. The monotony and arcing vasculature could suggest low grade fibromyxoid sarcoma, however that lesion should lack keratin staining and express MUC4. Pleura is a typical location for solitary fibrous tumor, however SFT should typically express CD34 and STAT6 and typically features “staghorn” vasculature. Sarcomatoid carcinoma of lung origin or other primary sites is a strong consideration and expression of keratin and TTF1 would support this diagnosis. A recent publication suggested that MUC4 positivity and GATA3 negativity can be used to support sarcomatoid carcinoma versus sarcomatoid mesothelioma in the setting of a malignant spindled tumor involving pleura. In this case, an epithelioid component was present in other sections and both components labeled with cytokeratin as well as multiple mesothelial markers, confirming the diagnosis of biphasic (epithelioid and sarcomatoid) mesothelioma.