Osteosarcoma arising in heterotopic ossification of dermatomyositis: case report and review of the literature.

A patient with dermatomyositis developed malignant transformation of the benign interfascial heterotopic bone. This patient had classic childhood dermatomyositis at the age of 3 years, and the disease was arrested after a one-year course of corticosteroid therapy. Extensive subcutaneous calcinosis cutis and deep interfascial calcinosis were the residua of the disease. Twenty-eight years later, the patient developed a high-grade osteosarcoma within the benign intermuscular heterotopic calcification and ossification that had been previously documented at the age of 8 years by a roentgenogram and at the age of 16 years by biopsy. This case represents the first report of the association of osteosarcoma and dermatomyositis, and possibly the first well-documented case of malignant transformation of benign heterotopic bone.