PGR and schwannoma: In such cases, ancillary tests, like immunohistochemical exams, play a key role in sorting the diagnostic quandary out: meningothelial tumors are usually positive for epithelial membrane antigen (EMA) and progesterone receptors (PR), while schwannomas and SFT/HPCs commonly stain respectively positive for S100 and SOX10 and for CD34 and STAT6.