Histologic and Immunohistochemical (Anti-CD34 antibody) analysis of sample obtained by transthoraxic Tru-cut biopsy give a confident preoperative diagnosis and exclude differential diagnosis like mesothelioma, fibrosarcoma, fibrous histiocytoma, fibromatosis, synovial sarcomas [3, 9]. The gene discussed is CD34; the disease is histiocytoma.