title: Quantitative analysis and diagnostic significance of methylated SLC19A3 DNA in the plasma of breast and gastric cancer patients.
abstract: BACKGROUND
  Previously, we have examined the methylation status of SLC19A3 (solute carrier family 19, member 3) promoter and found that SLC19A3 was epigenetically down-regulated in gastric cancer. Here, we aim to develop a new biomarker for cancer diagnosis using methylated SLC19A3 DNA in plasma.
  
  
  RESULTS
  SLC19A3 gene expression was examined by RT-qPCR. Methylation status of SLC19A3 promoter was evaluated by methylation-specific qPCR. SLC19A3 expression was significantly down-regulated in 80% (12/15) of breast tumors (P<0.005). Breast tumors had significant increase in methylation percentage when compared to adjacent non-tumor tissues (P<0.005). A robust and simple methylation-sensitive restriction enzyme digestion and real-time quantitative PCR (MSRED-qPCR) was developed to quantify SLC19A3 DNA methylation in plasma. We validated this biomarker in an independent validation cohort of 165 case-control plasma including 60 breast cancer, 45 gastric cancer patients and 60 healthy subjects. Plasma SLC19A3 methylated DNA level was effective in differentiating both breast and gastric cancer from healthy subjects. We further validated this biomarker in another independent blinded cohort of 78 plasma including 38 breast cancer, 20 gastric cancer patients and 20 healthy subjects. The positive predictive values for breast and gastric cancer were 90% and 85%, respectively. The negative predictive value of this biomarker was 85%. Elevated level in plasma has been detected not only in advanced stages but also early stages of tumors. The positive predictive value for ductal carcinoma in situ (DCIS) cases was 100%.
  
  
  CONCLUSIONS
  These results suggested that aberrant SLC19A3 promoter hypermethylation in plasma may be a novel biomarker for breast and gastric cancer diagnosis.
authors.affiliation: Department of Surgery, The University of Hong Kong, Hong Kong, Special Administrative Region, People's Republic of China.
authors.forename: Enders K O
authors.initials: EK
authors.lastname: Ng
authors.forename: Candy P H
authors.initials: CP
authors.lastname: Leung
authors.forename: Vivian Y
authors.initials: VY
authors.lastname: Shin
authors.forename: Chris L P
authors.initials: CL
authors.lastname: Wong
authors.forename: Edmond S K
authors.initials: ES
authors.lastname: Ma
authors.forename: Hong Chuan
authors.initials: HC
authors.lastname: Jin
authors.forename: Kent-Man
authors.initials: KM
authors.lastname: Chu
authors.forename: Ava
authors.initials: A
authors.lastname: Kwong
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics*; D008875:Middle Aged; D009367:Neoplasm Staging; D011401:Promoter Regions, Genetic / Q000235:genetics; D012372:ROC Curve; D015203:Reproducibility of Results; D013274:Stomach Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000235:genetics* / Q000473:pathology
chemical_list: D026901:Membrane Transport Proteins; C492291:SLC19A3 protein, human