Adamantinoma-like variant of Ewing sarcoma in the metatarsal bone after chemotherapy: Report of a case successfully treated with an osteocutaneous fibular transfer.

Adamantinoma-like Ewing sarcoma is a rare variant of Ewing sarcoma known to have histologic and immunohistochemical evidence of squamous differentiation. This variant most commonly occurs in the head and neck region with a few cases reported in long bones of the limbs. It may be associated with poorer clinical outcome and could pose a diagnostic challenge(s) particularly if it occurs in older patients or as a metastatic lesion. We present a case of Ewing sarcoma in the metatarsal of an 11 year old boy that manifested adamantinoma-like morphology after neo-adjuvant chemotherapy. Chemotherapy has been reported to induce neuronal maturation and rhabdoid morphology in cases of Ewing sarcoma, but no reports of treatment induced squamous differentiation with P40/P63 expression have been demonstrated. This is also the first documented case to use a pedicled osteocutaneous fibular transfer in a metatarsal malignancy, which is usually treated by either ray or below knee amputation.