Prostate-specific antigen flare phenomenon during 223Ra-Dichloride treatment for bone metastatic castration-resistant prostate cancer: a case report

223Ra-dichloride is an alpha-emitting radionuclide recently approved for for treatment of CRPC patients with symptomatic bone metastases. In this specific therapeutic setting, PSA is not an objective biomarker in assessing 223Ra efficacy. We present as case of a 79-years old patient affected by CRPC and symptomatic bone metastases enrolled in the 223Ra-dichloride Early Access Program who presented a relevant rise in PSA levels after the fifth 223Ra administration. No radiological signs of disease progression were found, so this event was recognized as a PSA flare phenomenon and last 223Ra infusion was administered. In clinical practice, PSA flare in the course of 223Ra treatment can be misinterpreted as a therapeutic failure with early withdrawal from a potentially effective therapy. During 223Ra treatment, PSA flare can be explained as a direct consequence of 223Ra cytotoxic effect on cancer cells. Further analysis should be conducted on large cohort in order to evaluate the clinical significance of PSA flare phenomenon during 223Ra treatme