Desmoplastic Fibroblastoma (Collagenous Fibroma)
Desmoplastic fibroblastoma (collagenous fibroma) is a benign fibrous tumor that usually presents as a slow-growing painless mass in the subcutaneous tissues or skeletal muscles of extremities. It is more common in males. Grossly, it is a firm, well-circumscribed mass with a uniform yellow or tan-white cut surface without hemorrhage or necrosis (as seen here). Microscopically, it is composed of bland spindle or stellate cells separated by abundant collagenous matrix. The tumor cells may show focal positivity for smooth muscle actin and muscle-specific actin. They are negative for desmin, CD34, S-100 protein, and cytokeratins. The differential diagnosis includes neurofibroma, calcifying fibrous pseudotumor, fibromatosis, low-grade fibromyxoid sarcoma, elastofibroma, and nodular fasciitis. Simple resection is curative treatment. There are no reports of recurrences or metastases.