[Highly malignant telangiectatic osteosarcoma. Long-term follow-up]

The teleangiectatic osteosarcoma is an extremely malignant tumor of the bone with rapid progression and short time of survival. In a 57 y.o. male such a tumor in the right proximal femur was diagnosed. Previously for 13 years a cystic bony lesion was known and followed in consequent intervals radiologically and clinically. There was no change in appearance till all at once malignant change developed. Systemic bone disease as ethiopathogenetic factor (e.g. ostitis deformans Paget) could be excluded. This case demonstrates an uncommon development of a teleangiectatic osteosarcoma out of a radiologically benign bony cyst, consequently followed for 13 years.