F13A1 and familial atrioventricular septal defect: Immunohistochemistry usually shows a characteristic staining profile of ECD cells (positive CD68, CD163, and factor XIIIa and negative CD1a and CD207), whereas S-100 positivity is rare.[18] Immunohistochemical analysis of BRAFV600E staining detected mutant protein in histiocytic neoplasms in more than 50% of ECD patients.