The flare phenomenon on radionuclide bone scan in metastatic prostate cancer.

The radionuclide bone scan 3 months after the initiation of treatment for advanced cancer of the prostate occasionally shows apparent progression of individual lesions despite clinical improvement. To determine the incidence and clinical significance of this so-called flare phenomenon, serial bone scans were reviewed in 33 patients with carcinoma of the prostate and bony metastases, who were receiving endocrine treatment for the first time. A flare reaction was seen in two (6%) of 33 bone scans obtained 3 months after initiation of treatment. A flare reaction on bone scan is an unusual phenomenon in prostatic cancer; in general, serial scans accurately depict the activity of bony metastases in these patients.