title: Free circulating DNA as a biomarker of prostate cancer: comparison of quantitation methods.
abstract: OBJECTIVE
  To identify a simpler method of free circulating DNA (fcDNA) quantitation that may improve the specificity of the prostate cancer prostate-specific antigen (PSA) screening test.
  
  
  METHODS
  The patient group consisted of 241 men with elevated PSA/abnormal digital rectal exam (DRE), undergoing prostate biopsy. Serum fcDNA levels were measured by UV absorbance and PicoGreen. Results were compared to previously published quantitative polymerase chain reaction (qPCR) data.
  
  
  RESULTS
  We found that levels of fcDNA measured by PicoGreen correlated well with those measured by qPCR (r=0.8552). In the patient group with PSA >4 to 10 ng/ml, those with fcDNA (PicoGreen) >53.1 ng/ml were at increased risk for prostate cancer compared to those with fcDNA ≤ 53.1 ng/ml. Moreover, we found that measuring fcDNA levels by PicoGreen does not compromise the negative predictive value, accuracy or specificity of the qPCR fcDNA test.
  
  
  CONCLUSIONS
  If validated in larger studies, PicoGreen quantitation of fcDNA could serve as a simple method to aid in prostate cancer diagnosis.
authors.affiliation: Sylvester Comprehensive Cancer Center, 1475 NW 12th Ave, Miami, FL-33136, U.S.A. rsingal@med.miami.edu.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Ramachandran
authors.forename: Carl G
authors.initials: CG
authors.lastname: Speer
authors.forename: Stephanie
authors.initials: S
authors.lastname: Fiddy
authors.forename: Isildinha M
authors.initials: IM
authors.lastname: Reis
authors.forename: Rakesh
authors.initials: R
authors.lastname: Singal
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000097:blood*; D001774:Blood Chemical Analysis; D004247:DNA / Q000097:blood*; D055088:Early Detection of Cancer / Q000379:methods; D005456:Fluorescent Dyes / Q000737:chemistry; D006801:Humans; D007610:Kallikreins / Q000097:blood; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009930:Organic Chemicals / Q000737:chemistry; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000097:blood* / Q000175:diagnosis; D012372:ROC Curve; D060888:Real-Time Polymerase Chain Reaction; D013056:Spectrophotometry, Ultraviolet
chemical_list: D014408:Biomarkers, Tumor; D005456:Fluorescent Dyes; D009930:Organic Chemicals; C099476:PicoGreen; D004247:DNA; C549870:KLK3 protein, human; D007610:Kallikreins; D017430:Prostate-Specific Antigen
keywords: PicoGreen; Prostate cancer; biomarker; cell-free DNA; quantitative PCR; screening