Flare phenomenon (bone scan)
Flare phenomenon or osteoblastic flare phenomenon refers to interval visualisation of lesions with a sclerotic rim around an initially lytic lesion or sclerosis of lesions previously undetected on radiograph or CT in the setting of follow-up of an oncological patient with other signs of partial response to treatment. It does not indicate disease progression but the healing of previously inconspicuous lesions.
On a bone scan, there is a spurious increase in radionuclide uptake because of reparative mineralisation around healing metastases. The phenomenon is typically seen between 2 weeks to 3 months following therapy, but can rarely be seen as late as 6 months after treatment. It is incorporated as part of MDA criteria of tumour response.
Treatment and prognosis
As it can be misinterpreted as progression in bone metastasis, so follow up bone scan for 6 months or more is the rule. If there is a subsequent decrease uptake in these lesions on repeat exam in 2-3 months, it then likely represents a flare phenomenon. If there is a continued increase in the number and intensity of lesions beyond 6 months, it is then usually indicative of disease progression.
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