Weak staining for CD45 was observed, while markers including cytokeratin AE1/AE3, S-100, CD3, CD5, CD10, CD15, CD20, CD30, CD34, and CD56 were negative, supporting the diagnosis of cutaneous histiocytic sarcoma (Figures 2, 3). Due to the lack of formal staging guidelines and the localized nature of the disease, the American Joint Committee on Cancer (AJCC) TNM (tumor, nodes, and metastasis) staging system for soft tissue sarcomas was applied, and the tumor was classified as stage IA. The gene discussed is CD5; the disease is neoplasm.