In detail, the diagnosis of HS requires positivity for CD163, CD68 (KP1 and PGM1), and lysozyme; and negativity for B cell- and T cell-lineage markers, typical Langerhans/Langerhans cell markers (CD1a, Langerin), follicular dendritic cells (CD21, CD23, CD35), epithelial markers (pan-cytokeratin), melanocytes (HMB-45, Melan A), and myeloid cells (CD13, CD33, myeloperoxidase). The gene discussed is ADA2; the disease is histiocytic sarcoma.