4. Radiological progression: a) New nodal, visceral or other soft tissue metastasis during the treatment with Abiraterone acetate and prednisone; b) increase of any target lesion >40% according to RECIST v1.1 criteria; c) any known visceral, nodal or soft tissue metastasis localisation causing symptomatic progression, and d) ≥ 3 new bone metastasis on bone-scan during treatment with abiraterone plus prednisone.