Metabolic and Prostate-Specific Antigen Response After Abiraterone Acetate Withdrawal: A New Clinical Scenario for Castration-Resistant Prostate Cancer?

Clinical Practice Points The availability of new drugs for castration-resistant prostate cancer patients might open new clinical scenarios that are unexpected. The withdrawal syndrome is a well known occurrence after antiandrogen therapy but is not described with use of the new drugs that act on androgen metabolism. It is usually unable to produce an instrumentally detectable improvement of the disease. We describe 2 cases of patients with castrationresistant, metastatic prostate cancer who experienced an abiraterone acetate (AA) withdrawal syndrome, and achieved a metabolic response. We obtained serial prostate-specific antigen (PSA) measurements and choline positron emission tomography/computed tomography (cPET/CT) scans to assess the patients’ response to AA withdrawal. The described patients stopped taking AA because of lack of biochemical response and progression occurrence visualized on cPET/CT scans. Before the start of new treatment, their PSA levels decreased and they remained using no therapy. After 3 months, we observed a progressive additional PSA reduction and a repeated cPET/CT scan revealed an improvement. This is the first report of a long-term withdrawal syndrome and a metabolic response after AA withdrawal. It seems to represent a rare new clinical scenario that might delay the introduction of additional treatment lines. Our findings suggest that it might also lead to a measurable improvement in disease.