[425] 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 and K-Ras Mutations Detected
EGFR mutation# Cases
Deletion in exon 191
K-Ras mutation# Cases
G12C & G13A1

Conclusions: Cytologic direct smears, routinely obtained during fine-needle aspirations, represent a valuable source of cellular material for molecular diagnostic studies and can be utilized in cases when a cell block exhibits insufficient cellularity or is not available. In our cohort of 33 cases of pulmonary adenocarcinoma, EGFR and KRAS mutations were detected at expected frequencies. Importantly, staining of the direct smears with Diff-Quik provides the opportunity for tumor cell enrichment by macrodissection and does not impair the ability to isolate high quality DNA for molecular studies. Archived or freshly collected cytologic smears are a viable, and in some cases, might be a preferred specimen source for molecular studies in pulmonary adenocarcinoma.
Category: Cytopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 81, Tuesday Morning


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