In the present case, significant hyperplasia of atypical tumor cells with a histologically acidophilic cytoplasm was found, and the patient was diagnosed with HS because the immunostaining was positive for CD68, CD163, CD4, CD5, CD15, and CD45 and negative for CD1a, CD21, CD34, MPO, and S-100 protein. The gene discussed is PTPRC; the disease is histiocytic sarcoma.