The Application of Molecular Diagnostic Studies Interrogating EGFR and KRAS Mutations to Stained Cytologic Smears of Pulmonary Adenocarcinoma.
Michael H Roh, Bryan L Betz, Helmut Weigelin, Jeremiah Placido, Lindsay Schmidt, Sara Farmen, Stewart M Knoepp. University of Michigan Medical School, Ann Arbor
Background: Cell blocks prepared from lung and mediastinal lymph node fine needle aspirates are routinely used for ancillary studies. Approximately 10% and 25% of pulmonary adenocarcinomas harbor mutations in epidermal growth factor receptor (EGFR) and KRAS, respectively. The most common EGFR mutations are in-frame deletions in exon 19 and the L858R substitution. KRAS mutations frequently involve codons 12, 13, and 61. Molecular diagnostic studies to interrogate these mutations are of increasing importance for gaining insight into prognosis and guiding the potential use of targeted chemotherapeutics. Unfortunately, in some cases, insufficient cellularity of cell blocks represents an impediment to the performance of these studies. Hence, we sought to investigate the utility of cellular material obtained from stained cytologic direct smears for EGFR and KRAS mutational analysis.
Design: Thirty-three cases of pulmonary adenocarcinoma (one air-dried, Diff-Quik stained direct smear per case) represented the source of material. Freshly collected and archived smears were used in 12 and 21 cases, respectively. Tumor cell-enriched areas from each smear were macrodissected for DNA isolation and purification. EGFR and KRAS mutational analysis was subsequently performed.
Results: The percentage of tumor cells in the extracted area on the direct smears ranged from 5 to 95% and exceeded 50% in the majority of cases (25 of 33; 76%). Sufficient yield of high quality DNA was obtained in all cases. EGFR and KRAS mutations were detected in three (9%) and 11 (33%) cases, respectively. EGFR and KRAS mutations were mutually exclusive.
|EGFR mutation||# Cases|
|Deletion in exon 19||1|
|K-Ras mutation||# Cases|
|G12C & G13A||1|