title: Clinical activity of abiraterone acetate in patients with metastatic castration-resistant prostate cancer progressing after enzalutamide.
abstract: BACKGROUND
  Abiraterone acetate and enzalutamide both improve outcomes in patients with metastatic castration-resistant prostate cancer (mCRPC). Optimal sequencing for these agents and whether cross-resistance occurs is unknown.
  
  
  METHODS
  Multicentre review of patients with mCRPC treated with abiraterone acetate and prednisone after progressing on enzalutamide. Primary objective was to determine abiraterone acetate response.
  
  
  RESULTS
  Thirty patients identified from four North American centres. At abiraterone initiation, median age was 70 years (56-84 years); 70% had ECOG performance status of 0-1; all had prior docetaxel. Median prior enzalutamide treatment duration was 41 weeks (6-95 weeks), with 70% (21 of 30) having a ≥30% prostate-specific antigen (PSA) decline. Median abiraterone acetate treatment duration was 13 weeks (1-52). No objective radiographic responses were observed. Median abiraterone time to progression (PSA, objective or symptomatic) was 15.4 weeks [95% confidence interval (CI) 10.7-20.2]. Median overall survival was 50.1 weeks (95% CI 28.3-72.0). Three patients had a ≥30% PSA decline with abiraterone. Two of these patients had PSA progression as best response with prior enzalutamide.
  
  
  CONCLUSIONS
  In this study of patients progressing after enzalutamide, treatment with abiraterone was associated with a modest response rate and brief duration of effect. Primary progression on enzalutamide may not preclude a response to abiraterone.
authors.affiliation: Department of Medical Oncology, BC Cancer Agency, Vancouver Cancer Centre, Vancouver.
authors.forename: K L
authors.initials: KL
authors.lastname: Noonan
authors.affiliation: Department of Medical Oncology, Cross Cancer Institute, Edmonton, Canada.
authors.forename: S
authors.initials: S
authors.lastname: North
authors.affiliation: Duke Cancer Institute and the Duke Prostate Center, Duke University, Durham, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Bitting
authors.affiliation: Duke Cancer Institute and the Duke Prostate Center, Duke University, Durham, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Armstrong
authors.affiliation: Department of Medical Oncology, BC Cancer Agency, Cancer Centre for the Southern Interior, Kelowna, Canada.
authors.forename: S L
authors.initials: SL
authors.lastname: Ellard
authors.affiliation: Department of Medical Oncology, BC Cancer Agency, Vancouver Cancer Centre, Vancouver. Electronic address: kchi@bccancer.bc.ca.
authors.forename: K N
authors.initials: KN
authors.lastname: Chi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000736:Androstenes; D000737:Androstenols / Q000627:therapeutic use*; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001549:Benzamides; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000556:secondary; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007610:Kallikreins / Q000097:blood; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009570:Nitriles; D010669:Phenylthiohydantoin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D016032:Randomized Controlled Trials as Topic; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D000736:Androstenes; D000737:Androstenols; D000970:Antineoplastic Agents; D001549:Benzamides; D009570:Nitriles; D010669:Phenylthiohydantoin; C540278:enzalutamide; C549870:KLK3 protein, human; D007610:Kallikreins; D017430:Prostate-Specific Antigen; C089740:abiraterone
keywords: abiraterone acetate; castration-resistant; enzalutamide; prostatic neoplasms