title: Natural history of small index lesions suspicious for prostate cancer on multiparametric MRI: recommendations for interval imaging follow-up.
abstract: OBJECTIVE
  We aimed to determine the natural history of small index lesions identified on multiparametric-magnetic resonance imaging (MP-MRI) of the prostate by evaluating lesion-specific pathology and growth on serial MP-MRI.
  
  
  METHODS
  We performed a retrospective review of 153 patients who underwent a minimum of two MP-MRI sessions, on an institutional review board-approved protocol. Index lesion is defined as the lesion(s) with the highest cancer suspicion score based on initial MP-MRI of a patient, irrespective of size. Two study cohorts were identified: (1) patients with no index lesion or index lesion(s) ≤7 mm and (2) a subset with no index lesion or index lesion(s) ≤5 mm. Pathological analysis of the index lesions was performed following magnetic resonance/ultrasound fusion-guided biopsy. Growth rate of the lesions was calculated based on MP-MRI follow-up.
  
  
  RESULTS
  Patients with small index lesions measuring ≤7 mm (n=42) or a subset with lesions ≤5 mm (n=20) demonstrated either benign findings (86.2% and 87.5%, respectively) or low grade Gleason 6 prostate cancer (13.8% and 12.5%, respectively) on lesion-specific targeted biopsies. These lesions demonstrated no significant change in size (P = 0.93 and P = 0.36) over a mean imaging period of 2.31±1.56 years and 2.40±1.77 years for ≤7 mm and ≤5 mm index lesion thresholds, respectively. These findings held true on subset analyses of patients who had a minimum of two-year interval follow-up with MP-MRI.
  
  
  CONCLUSIONS
  Small index lesions of the prostate are pathologically benign lesions or occasionally low-grade cancers. Slow growth rate of these small index lesions on serial MP-MRI suggests a surveillance interval of at least two years without significant change.
authors.affiliation: Urologic Oncology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA. soroush.rais-bahrami@nih.gov.
authors.forename: Soroush
authors.initials: S
authors.lastname: Rais-Bahrami
authors.forename: Barış
authors.initials: B
authors.lastname: Türkbey
authors.forename: Ardeshir R
authors.initials: AR
authors.lastname: Rastinehad
authors.forename: Annerleim
authors.initials: A
authors.lastname: Walton-Diaz
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Hoang
authors.forename: M Minhaj
authors.initials: MM
authors.lastname: Siddiqui
authors.forename: Lambros
authors.initials: L
authors.lastname: Stamatakis
authors.forename: Hong
authors.initials: H
authors.lastname: Truong
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Nix
authors.forename: Srinivas
authors.initials: S
authors.lastname: Vourganti
authors.forename: Kinzya B
authors.initials: KB
authors.lastname: Grant
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Merino
authors.forename: Peter L
authors.initials: PL
authors.lastname: Choyke
authors.forename: Peter A
authors.initials: PA
authors.lastname: Pinto
mesh_terms: D000368:Aged; D015331:Cohort Studies; D003287:Contrast Media; D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans; D007089:Image Enhancement; D061705:Image-Guided Biopsy; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011467:Prostate / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology*; D012189:Retrospective Studies
chemical_list: D003287:Contrast Media