RESUMEN
A case of osteosarcoma in pelvic bone following radiation therapy for prostate cancer is reported. A 74-year-old patient was diagnosed with prostate cancer 10 years ago and started on the endocrine therapy with LH-RH agonist. He had no apparent distant metastasis, and received radiation therapy 8 years ago. He has complained of low back pain since several months ago. A high uptake on bone scintigram and osteolytic and osteoblastic damages on CT were noted in pubic bone and sacrum. The PSA level was less than 0.2 ng/ml. Pathohistological diagnosis by biopsy of the pubic bone was chondroblastic type osteosarcoma, showing an atypical cell proliferation with osteoid. Immunostaining for nonepithelial marker vimentin was positive. He underwent heavy ion radiation therapy for osteosarcoma at the National Institute of Radiological Sciences. Osteosarcoma is one of the rare delayed complications after radiation therapy and requires biopsy for correct diagnosis.