Flare phenomenon or osteoblastic flare phenomenon refers to interval visualization 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 bone scintigraphy, there is a spurious increase in radionuclide uptake because of reparative mineralization 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 the MD Anderson (MDA) criteria of response of bone metastases to treatment.
Treatment and prognosis
As it can be misinterpreted as progression in bone metastasis, follow up bone scintigraphy 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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