{"entity":{"id":"flare-phenomenon","kind":"term","name":"Flare phenomenon","aka":[],"tldr":"Right after some cancer treatments start working, a scan can briefly look worse before it looks better, because healing bone or an early immune response makes lesions light up more, not because the cancer has actually grown. Doctors wait and repeat the scan before deciding treatment has failed.","summary":"The flare phenomenon (bone flare or scintigraphic flare) is an apparent early worsening on a bone scan, PET or PSMA-PET scan that reflects a reparative or reactive process rather than true disease progression, and is followed by genuine improvement on later imaging if the underlying treatment is actually working. On technetium-99m bone scintigraphy it appears as new or more intense uptake at existing or previously inconspicuous lesions, driven by reparative osteoblastic mineralisation around healing metastases as bone lesions respond to hormone therapy, chemotherapy or bone-seeking radiopharmaceuticals; it typically appears between two weeks and three months after starting treatment, occasionally as late as six months. Reported incidence varies widely: series in patients starting first-line hormone therapy for metastatic prostate cancer describe flare in roughly 6-41% of patients depending on definition and timing of the repeat scan, and around 10% of patients receiving bone-seeking radiopharmaceutical therapy (strontium-89, samarium-153, rhenium-186, and radium-223) show a comparable flare pattern.\n\nBecause flare can be mistaken for progression, standard practice (reflected in the MD Anderson bone response criteria) is to continue therapy for a minimum of roughly 12 additional weeks before concluding a scan reflects true progression, and to confirm any apparent worsening with a repeat scan 2-3 months later showing subsequent improvement, rather than acting on a single early scan. A parallel phenomenon, PSA flare (a transient early rise in prostate-specific antigen after starting androgen deprivation therapy or antiandrogens, from an initial agonist effect before suppression takes hold), is a distinct biochemical marker that does not always occur together with bone flare; in one series both bone and PSA flare co-occurred in only about one in four patients showing either.\n\nOn PSMA-PET, flare has been studied less consistently: one cohort study found no clear PSMA expression flare after starting androgen-receptor-pathway inhibitors, while retaining the possibility that a short-duration or very early flare could have been missed, so PSMA-PET response assessment guidance generally still recommends confirmatory follow-up imaging before calling early progression, particularly close to treatment initiation.","asOf":"2026-09-22","links":[{"label":"Conteduca V, et al. Flare phenomenon in prostate cancer: recent evidence on new drugs and next generation imaging, Ther Adv Med Oncol 2021","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC7907710/"},{"label":"Radiopaedia: Flare phenomenon (bone scintigraphy)","url":"https://radiopaedia.org/articles/flare-phenomenon-bone-scintigraphy?lang=us"},{"label":"Flare phenomenon visualized by 99mTc-bone scintigraphy has favourable prognostic value in mCRPC, Ann Nucl Med 2024","url":"https://link.springer.com/article/10.1007/s12149-024-01914-8"}],"tags":["response assessment","bone imaging","prostate cancer"],"related":["bone-metastases","psa-kinetics","prostate-mcrpc","psma-pet","radium-223","complete-response-term","tc-99m","ra-223","sm-153","sr-89"],"indications":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"imaging"},"route":"/terms/flare-phenomenon/","neighbours":{"term":[{"id":"bone-metastases","kind":"term","name":"Bone metastases and skeletal-related events","route":"/terms/bone-metastases/"},{"id":"complete-response-term","kind":"term","name":"Complete response (CR) and partial response (PR)","route":"/terms/complete-response-term/"},{"id":"psa-kinetics","kind":"term","name":"PSA kinetics: PSA doubling time and PSA density","route":"/terms/psa-kinetics/"}],"indication":[{"id":"prostate-mcrpc","kind":"indication","name":"Metastatic castration-resistant prostate cancer","route":"/indications/prostate-mcrpc/"}],"technology":[{"id":"psma-pet","kind":"technology","name":"PSMA PET","route":"/technologies/psma-pet/"}],"drug":[{"id":"radium-223","kind":"drug","name":"Radium-223 dichloride","route":"/drugs/radium-223/"}],"isotope":[{"id":"ra-223","kind":"isotope","name":"Radium-223","route":"/isotopes/ra-223/"},{"id":"sm-153","kind":"isotope","name":"Samarium-153","route":"/isotopes/sm-153/"},{"id":"sr-89","kind":"isotope","name":"Strontium-89","route":"/isotopes/sr-89/"},{"id":"tc-99m","kind":"isotope","name":"Technetium-99m","route":"/isotopes/tc-99m/"}]}}