Osteosarcoma, fibrous dysplasia, and a chromosomal abnormality in a 3-year-old child.

Osteosarcoma is a type of malignant bone tumor that is rare among children less than five years old. This report describes a 3-year-old boy with osteosarcoma of the right proximal femur and polyostotic fibrous dysplasia of the right femur and tibia. After hemipelvectomy, histologic examination of the amputated limb disclosed that the osteosarcoma had developed in a focus of fibrous dysplasia. Cytogenetic analysis of the patient's blood lymphocytes revealed a 4q-/7p + translocation in all cells. The patient's mother had an identical translocation but did not have a history of osteosarcoma or evidence of fibrous dysplasia. The chromosomal abnormality and the developmental osseous disorder may have predisposed this patient to developing osteosarcoma at an exceptionally young age.