DNA Extracted from Cytologic Slides Is a Valuable Source for PCR-Based Molecular Tests

Abstract

Introduction: DNA extracted from cytologic samples is occasionally used for various molecular tests. The aim of this study was to evaluate DNA extracted from differently prepared cytologic slides that can be used for PCR-based molecular tests. Methods: For each 23 cases of papillary thyroid carcinoma or colorectal adenocarcinoma tissues, six touch-imprinted cytological slides were prepared (group 1∼3), and remnant tissues were blocked for FFPE tissue (group 4). Cytologic slides were grouped by preparation methods: air-dried slides (group 1), fixed slides (group 2), and stained slides (group 3). Fixed slides were classified as 95% ethanol fixed (group 2A) and CytoRich Red Preservative solution fixed (group 2B). Stained slides were divided in 3 ways: Giemsa, Pap, and H&E stained (group 3A, 3B, and 3C, respectively). DNA extracted from each group was evaluated for concentration, 260/280 ratio, DNA Integrity Number (DIN) value, and mutation. Results: DNA concentration was highest in group 1 and lowest in group 2B. DIN value was highest in group 2A and lowest in group 2B. A mutation of BRAF or KRAS genes was detected in 18 FFPE tissue samples. Matched DNA extracts from groups 1, 2A, and 3 produced results consistent with FFPE tissue results, while mutation testing was successful for only four samples of DNA from group 2B. Conclusion: The mutation tests worked well for most samples except CytoRich Red Preservative-fixed slides. This study indicates that stained and unstained cytologic slides are a suitable source of PCR-based molecular tests as long as they are fixed in ethanol or stored for a short time in an air-dried condition.