A 3 1/2-year-old boy had thigh pain and a leg mass. Bone scanning demonstrated intense uptake within the involved femur, but no uptake within the soft tissues or evidence of metastatic spread. Radiographs and CT scanning showed a large soft tissue mass and periosteal reaction suggestive of Ewing's sarcoma. Following chemotherapy, the patient had an apparently good clinical response. However, bone scanning showed uptake that was more intense and extensive than it was before therapy. Plain films and CT showed that the uptake was evidence of soft tissue calcification and that the mass had shrunk.This is an unusual example of the flare response to therapy because the apparent progression of the disease on bone scanning was caused by extraskeletal uptake.
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