Familial occurrence of telangiectatic osteosarcoma: cousin cases.

Familial occurrence of osteosarcoma is rare. We report cousin cases, an 11-year-old girl and an 8-year-old boy with telangiectatic osteosarcoma. The tumors occurred in the metaphysis of the distal tibia and the lamina of thoracic vertebra. The local behaviors appeared aggressive, but the clinical courses were relatively indolent in both cases. The histologic features were similar, showing anaplastic tumor cells producing osteoid and proliferation of blood cavities. Clustering of malignancies within a family suggests the presence of a genetic factor.