The Utilization of Stained Cytologic Direct Smears for ALK Rearrangement Testing of Lung Adenocarcinoma
Bryan L Betz, Catherine A Dixon, Helmut C Weigelin, Stewart M Knoepp, Michael H Roh. University of Michigan Health System, Ann Arbor, MI; St. Joseph Mercy Health System, Ann Arbor, MI
Background: Advances in our understanding of the molecular landscape of non-small cell lung cancer (NSCLC) has provided opportunities for targeted therapeutics. Rearrangements involving the ALK gene are present in approximately 5% of NSCLC. Crizotinib has been recently approved for the treatment of NSCLCs harboring ALK rearrangements. A large number of patients with lung cancer are diagnosed at high stage and are not candidates for surgical resection of their primary tumors. For these patients, cytologic specimens often represent the only tumor samples available for tissue diagnoses and necessary molecular studies. Cell block (CB) preparations are routinely used for molecular studies. However, insufficient cell block cellularity, in some instances, can impede the performance of these assays.
Design: Paired Diff-Quik stained smears and corresponding CB sections from 23 cytology cases of lung adenocarcinoma were analyzed by fluorescence in-situ hybridization (FISH) for ALK rearrangement. Prior to testing, the smears were examined to identify tumor cell enriched areas that were marked using a diamond-tipped scribe, decoverslipped in xylene, and then destained in acid-alcohol.
Results: Paired ALK rearrangement analysis by FISH was successful for all 23 cases. An ALK rearrangement was detected on direct smears and CB sections in 4 (17%) and 3 (13%) of 23 cases, respectively. Concordant FISH results for smears and CBs were observed in 22 (96%) of 23 cases. In the one discordant case, an ALK rearrangement was detected on the direct smear but not in the CB. RT-PCR analysis of this CB revealed the presence of an EML4-ALK rearrangement, confirming a false negative FISH result in the CB section.
Conclusions: Stained cytologic direct smears can be effectively utilized for ALK rearrangement analysis by FISH. This approach represents a useful safeguard when insufficient CB cellularity is encountered. Based on our experience detailed herein in conjunction with prior reports regarding the utilization of direct smears for other molecular applications, complementary methods of cytologic specimen triage for molecular testing will be presented. An overall triage mechanism that incorporates safeguards has the potential to prevent repeat procedures, for which sufficient CB cellularity is not necessarily guaranteed, and prevent delays in treatment in this era of precision medicine.
Tuesday, March 5, 2013 1:30 PM
Proffered Papers: Section C, Tuesday Afternoon