Patients with non-small cell lung cancer (NSCLC) positive for anaplastic lymphoma kinase (ALK) gene rearrangements may be treated successfully with the ALK inhibitor crizotinib. ALK copy-number abnormalities have also been described. In this study, we evaluated the suitability of fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) to determine ALK status in endobronchial ultrasound (EBUS)-derived cytology samples.
Samples were obtained from 55 consecutive patients with NSCLC who had undergone EBUS-transbronchial needle aspiration (TBNA) according to our standard clinical protocols. All tumours had been screened previously for epithelial growth factor receptor (EGFR) and v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations. FISH, using commercially available ALK rearrangement-specific probes, was employed to assess ALK status. IHC using the ALK-1 monoclonal antibody (DAKO) was also performed.
FISH analysis was successful in 52 of 55 samples (94.5%); ALK rearrangement was demonstrated in 3 of 52 samples from patients with NSCLC (5.7%). ALK amplification was observed in 3 of 52 patient samples (5.7%) and an increase in ALK copy number was found in 28 of 52 patient samples (53.8%). IHC on cell blocks demonstrated ALK expression in one of three samples with ALK rearrangement. One patient sample had concomitant ALK rearrangement and KRAS mutation.
We found FISH to be superior to IHC using the ALK-1 monoclonal antibody for the detection of ALK rearrangement in EBUS-TBNA cytology specimens in NSCLC, and also that ALK rearrangement can co-exist with KRAS mutation in the same tumour.