ALK translocation detection in non-small cell lung cancer cytological samples obtained by TBNA or EBUS-TBNA

As the diagnosis of non-small cell lung cancer (NSCLC) is based on cytology in around 70% of cases, it is important to use the same material for molecular analyses. Fluorescence in situ hybridization (FISH) is the only approved test for the detection of the translocation and inversion of anaplastic lymphoma kinase (ALK), but the optimal procedures for the fixation or staining of the sample before FISH evaluation have not been established. We investigated whether ALK gene status determined by FISH in a prospectively enrolled case series of patients was affected by fixation and staining.

One hundred and fifteen cytological samples were obtained by transbronchial needle aspiration (TBNA) or endobronchial ultrasound (EBUS)-TBNA from 109 patients with NSCLC. All samples were evaluated for epidermal growth factor receptor (EGFR) mutation by pyrosequencing and for ALK rearrangement by FISH. Specimens for ALK determination had been fixed with Cytofix(®) and/or Carnoy's solution or 10% formalin (cell blocks) and variously stained.

Sixteen (14%) of the 115 samples were mutated for EGFR and 99 (86%) showed wild-type EGFR status. Of these 115 samples, 79 (69%) were negative for echinoderm microtubule-associated protein like 4 (EML4)-ALK translocation, nine (8%) were positive and 27 (23%) were unevaluable. In particular, 19 (26%) of the 72 Papanicolaou-stained smears fixed with Cytofix were unevaluable because of inadequate samples or cell overlapping; neither of the two May-Grünwald-Giemsa-stained samples were evaluable. Ten of 17 smears used for rapid on-site evaluation (ROSE) and immediately post-fixed in Carnoy's solution or 80% alcohol were evaluable.

In this series, smears were unevaluable as a result of inadequate samples, cell overlapping or lack of fixation performed immediately after FNA.