Usefulness of cytological samples (CS) for the assessment of ALK rearrangements in non-small cell lung cancer (NSCLC).

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e18008 Background: ALK gene rearrangements define a new molecular subtype of NSCLC with response to Crizotinib, a dual MET and ALK inhibitor. Analysis of ALK rearrangements has been performed in biopsies or surgical specimens. However, advanced NSCLC is often diagnosed by FNA cytology obtained through minimally invasive techniques, and frequently CS are the only tumour sample available. We assessed the feasibility of determining ALK rearrangements in CS. Methods: We studied prospectively ALK rearrangements in 53 CS from 53 NSCLC patients (30 M/23 F) by FISH (Vysis dual colour break apart probe). We considered positive for ALK rearrangement when > 15% of cells show splits signals. Tumor samples were obtained by bronchoscopy -FNA in 26 cases (49.1%), EBUS-FNA in 7 (13.2%), EUS-FNA in 3 cases (5.7%), CT-FNA in 3 (5.7%), and direct FNA in 6 cases (11.3%). Two cavity fluids (3.8%), 4 imprints (7.5%), and 2 cellblocks received for consultation (3.8%) were also studied. FISH was performed on non-stained ThinPrep in 28 cases (52.8%), Papanicolau stained smears in 15 cases (28.3%), cell block in 9 cases (17%), and 1 stained ThinPrep. All cases were tested for EGFR and KRAS mutations. Correlation cytological/paraffin embedded samples was performed in 4 paired cases. Results: Thirty-seven samples(69.8%) were adequate for FISH analysis. Three cases (8.1%) had ALK rearrangements: non-smoker women with adenocarcinoma, two of them with signet ring cells. One case had a concurrent EGFR mutation in exon 21. FISH study was unsuccessful in 16 cases (30.2%):10 Papanicolau stained smears (62.5%), 5 unstained ThinPrep (31.3%), and 1 cell block. Nineteen ThinPrep slides were adequate for FISH analysis (86.4%) as well as 8 out of 9 cell blocks. Concordance rate in paired cases were 100%. Conclusions: Determination of ALK gene rearrangements in CS is feasible. It is mandatory an exquisite management and care of the samples to preserve quality. ThinPrep and cell blocks are the most suitable samples for FISH analysis, while Papanicolau stained smears provide poor results. Coexistence of ALK gene rearrangements and EGFR mutations was observed in one case, indicating that such alterations are not necessarily mutually exclusive.