Malignancy of Aneurysmal Bone Cyst in Osteosarcoma and Angiosarcoma: Series of 2 Cases and Literature Review

Aneurysmal bone cyst (ABC) is a rare benign bone tumor characteristic of the first decades of life. Malignization of ABC in the absence of risk factors such as radiotherapy is extremely rare, with few cases published in the literature. There are malignant tumors such as telangiectatic osteosarcoma with an initial clinical, radiological and anatomopathological resemblance that requires special attention in their differential diagnosis. We present two patients with an initial histologic diagnosis of ABC who developed true malignancy, in the absence of risk factors, into osteoblastic osteosarcoma and epithelioid angiosarcoma. In spite of its exceptional nature, in the presence of an aggressive type of ABC malignant degeneration should always be suspected and therefore, an open biopsy and wide resection performed for a correct diagnosis to avoid residual microscopic disease in case of aggressiveness. Epithelioid angiosarcoma from an ABC tumor malignancy has never been described before.