Table 1.

The initial differential diagnoses and their histological and immunohistochemical features

Diagnoses	Histological features	Immunohistochemical features
Leiomyoma	Interlacing bundles of bland spindle cells with eosinophilic cytoplasm and blunt-ended, cigar-shaped, vesicular nuclei. Necrosis and mitosis are absent	Diffusely and strongly positive for α-smooth muscle actin
Dermatofibrosarcoma protuberans	Fairly uniform spindle cells with elongated nuclei showing little pleomorphism and pale cytoplasm, arranged in storiform or “rush mat” pattern	Usually diffusely positive for CD34, negative for S-100, desmin and α-smooth muscle actin
Leiomyosarcoma	Infiltrative tumor composed of interlacing bundles of cells with eosinophilic cytoplasm and blunt-ended, cigar-shaped, often vesicular nuclei. Varied cytological pleomorphism	Diffusely positive for α-smooth muscle actin, desmin and h-caldesmon, negative for S-100 and CD34
Malignant peripheral nerve sheath tumors	Alternating myxoid and cellular areas containing irregular interlacing bundles of spindle cells with scanty pale cytoplasm and wavy, hyperchromatic, variably pleomorphic nuclei. Myxoid change, hyaline nodule and perivascular whorling may be present	50% of these tumors are S-100 positive, negative for α-smooth muscle actin
Malignant phyllodes tumor	Epithelial slits and hypercellular stroma showing marked overgrowth of spindle cells. Prominent nuclear pleomorphism, mitotic count over 10 per 10 HPF and infiltrative tumor border	Spindle cells are positive for vimentin and negative or only focally positive for α-smooth muscle actin. Positive staining for CD117 was reported
Malignant fibrous histiocytoma	Prominently pleomorphic cells arranged in storiform pattern. Bizarre multinucleated giant cells, and a mononuclear inflammatory cell infiltrate with foamy macrophages are often present. Most represent extension from deep soft tissue	Negative for α-smooth muscle actin
Sarcomatoid carcinoma	A tumor composed of markedly atypical spindle and pleomorphic epithelial cells, necrosis, and numerous atypical mitotic figures	Pleomorphic spindle cells are positive for cytokeratin, negative for α-smooth muscle actin
Spindle cell malignant melanoma	Groups of spindle cells exhibiting variable pigmentation and pleomorphism	Stain positively for S-100 protein and HMB45, negative for α-smooth muscle actin