title: Use of touch imprint cytology as a simple method to enrich tumor cells for molecular analysis.
abstract: BACKGROUND
  A relative excess of nonneoplastic cells in frozen carcinoma samples is often a cause of false-negative results in molecular assays. Given the greater cohesiveness of epithelial tumor cells compared with nonneoplastic epithelium and mesenchymal stroma, the authors hypothesized that tumor procurement by touch imprinting would provide a simple, cost-effective method of obtaining enriched neoplastic cells compared with frozen whole-tumor samples.
  
  
  METHODS
  Eleven adenocarcinomas with known KRAS gene mutations were tested. Two sets of 8 touch imprint (TP) slides and 1 frozen whole-tumor sample (FS), both with a corresponding hematoxylin and eosin-stained slide, were obtained from each tumor. DNA from unstained TP and FS samples was tested for KRAS exon 2 mutations by Sanger sequencing. The percentage of carcinoma cells was determined by light microscopy of hematoxylin and eosin-stained slides. The fold increase in the mutant-enriched DNA in TP versus FS samples was determined by calculating the height ratio between the mutant and wild-type peaks on the sequencing electropherogram.
  
  
  RESULTS
  Using light microscopy, TP demonstrated a 1.1-fold to 3.5-fold (mean, 1.8-fold) enrichment in neoplastic cells compared with the FS. The mutant-to-wild-type peak height ratio was 1.4-fold to 7.1-fold (mean, 3.1-fold) higher in TP compared with the corresponding FS samples. The average amount of extracted DNA ranged from 145 ng to 7.9 μg per TP slide.
  
  
  CONCLUSIONS
  The procurement of carcinoma samples by TP is rapid, simple, and inexpensive; consistently provides a tumor-enriched sample; is an excellent source of high-quality tumor DNA; and could compensate for the relatively low sensitivity of direct sequencing. Cancer (Cancer Cytopathol) 2013;121:354-360. © 2013 American Cancer Society.
authors.affiliation: Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
authors.forename: Snjezana
authors.initials: S
authors.lastname: Dogan
authors.forename: Jillian C
authors.initials: JC
authors.lastname: Becker
authors.forename: Natasha
authors.initials: N
authors.lastname: Rekhtman
authors.forename: Laura H
authors.initials: LH
authors.lastname: Tang
authors.forename: Khedoudja
authors.initials: K
authors.lastname: Nafa
authors.forename: Marc
authors.initials: M
authors.lastname: Ladanyi
authors.forename: David S
authors.initials: DS
authors.lastname: Klimstra
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology*; D021441:Carcinoma, Pancreatic Ductal / Q000235:genetics / Q000473:pathology*; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology*; D003581:Cytodiagnosis / Q000379:methods / Q000706:statistics & numerical data*; D004252:DNA Mutational Analysis; D004273:DNA, Neoplasm / Q000032:analysis* / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000556:secondary*; D008175:Lung Neoplasms / Q000235:genetics / Q000556:secondary*; D009154:Mutation / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins / Q000235:genetics
chemical_list: D004273:DNA, Neoplasm; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
keywords: Sanger sequencing; molecular analysis; touch imprint cytology; tumor enrichment; tumor procurement