This disease has a predilection for the distal femur, proximal tibia, and proximal humerus. The patient presents with a hard, painless mass.
Alkaline phosphatase is normal.
The tumor shows slow, indolent growth with eventual invasion of the underlying bone. There may be a late growth spurt with dedifferentiation into a high-grade lesion. Late pulmonary metastasis occurs in 10 percent of the uncontrolled lesions. This is a radiograph of an asymptomatic, Stage I-A parosteal osteosarcoma of the distal femur for which no treatment was given. At follow-up one year later, there was no change.