A case of radiation-induced osteosarcoma of the skull presenting as a cutaneous epidermotropic tumor with a short latent period.

Radiation-induced sarcoma (RIS) is an unusual but well documented tumor. The frequency of RIS of the head and neck region has been reported as 0.143%. In the literature the median interval between irradiation and development of sarcoma is 11 years. Cases of RIS with a short latent period, that is, less than 4 years are rare. We report a case of a 34-year-old female who developed an osteosarcoma of the scalp, over a previous craniotomy scar, 3 years after excision of a frontal anaplastic oligodendroglioma which had been followed by a course of 6 weeks radiotherapy (58 Gy) and 6 cycles of temozolomide. The histological features were those of a high-grade osteosarcoma with epidermotropism of tumor cells. Lymph nodes were partially replaced by high-grade metastatic osteosarcoma, with extra-nodal lymphatic tumor thrombi. To our knowledge the only other case report of post-radiation osteosarcoma with a short latency period was a case of osteosarcoma in the craniofacial bone 3 years after radiotherapy for maxillary squamous cell carcinoma. The histological finding of prominent replacement of the epidermis by osteosarcoma has not been reported before.