Case report: Natural development of osteosarcoma from precancerous lesion

We encountered a very rare case that suggested the natural development of o steosarcoma from a precancerous lesion. The patient presented with a huge o steosarcoma in the distal femur on the initial consultation to our hospital . He had undergone X-ray examination twice previously: due to a knee injury . The findings of the lesion detected by the first X-ray examination were s imilar to a fibrous cortical defect (FCD), differing from those of an osteo sarcoma lesion detected by second and last X-ray examinations. We retrospec tively estimated the growth rate of the FCD-like and osteosarcoma lesions a nd found that FCD-like lesion was not osteosarcoma, but might have been a p recancerous lesion. We also speculated that this osteosarcoma lesion might have appeared 18 months before the patient consulted our hospital.