Volume 5 • Issue 2 • 1000216 J Cytol Histol ISSN: 2157-7099 JCH, an open access journal Research Article Open Access Cooper and O’Toole, J Cytol Histol 2014, 5:2 DOI: 10.4172/2157-7099.1000216 Review Article Open Access Detecting ALK Gene Rearrangements in Lung Cancer Cytology Specimens Cooper WA 1-3 and O’Toole SA 1,2,4 1 Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia 2 Sydney Medical School, University of Sydney, NSW, Australia 3 School of Medicine, University of Western Sydney, NSW, Australia 4 The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia *Corresponding author: Wendy Cooper, Department of Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Missenden Rd, Camperdown NSW 2050, Australia, Tel: (+612) 9515 7804; Fax: (+612) 9515 8405; E-mail: Wendy.Cooper@sswahs.nsw.gov.au Received January 23, 2014; Accepted February 04, 2014; Published February 06, 2014 Citation: Cooper WA, O’Toole SA (2014) Detecting ALK Gene Rearrangements in Lung Cancer Cytology Specimens. J Cytol Histol 5: 216. doi:10.4172/2157- 7099.1000216 Copyright: © 2014 Cooper WA, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Molecular testing for EGFR mutations and ALK gene rearrangements has become a routine part of lung cancer pathological diagnosis, and is critical to determine the most effective therapies for patients with this poor prognosis cancer. ALK gene rearrangements are seen particularly in adenocarcinoma of the lung and are associated with an excellent response rate to targeted inhibition with crizotinib in clinical trials for many patients whose tumours harbour this change. ALK gene rearrangement is generally observed at low incidence posing challenges for routine detection. Since a high proportion of lung cancers are inoperable at presentation, cytology plays a central role in diagnosis and provision of material for ALK testing. The advantages offered by cytology specimens for ALK and other molecular testing are becoming increasingly recognised - cytology specimens tend to have a lower proportion of contaminating stromal and other non-neoplastic cells and often have higher quality DNA than routine histology specimens. One challenge is the often limited amount of cytological material obtaining in many lung cancer cytology specimens. FISH testing for ALK gene rearrangement using a break-apart probe is the gold standard for testing although there is a strong role for immunohistochemistry in ALK testing. This review highlights key aspects of ALK testing in cytology specimens. Keywords: Lung adenocarcinoma; ALK, Anaplastic lymphoma kinase; FISH; Immunohistochemistry Abbreviations: ALK: Anaplastic Lymphoma Kinase; EML4: Echinoderm Microtubule Associated Protein-like 4; FISH: Fluorescent in situ Hybridization; IHC: Immunohistochemistry; NSCLC: Non- Small Cell Lung Carcinoma; NOS: Not Otherwise Specifed; RT-PCR: Reverse-Transcriptase Polymerase Chain Reaction; TKI: Tyrosine Kinase Inhibitor Introduction Accurate subtyping of non-small cell lung carcinoma (NSCLC) is important due to implications for treatment selection and due to the unique mutational profle of diferent lung cancer subtypes [1]. Adenocarcinomas, tumours with an adenocarcinoma component or NSCLC- not otherwise specifed (NOS) (in cytology or small biopsy samples) may harbour driver mutations amenable to targeted therapy [2]. It is estimated that about 70% of patients with NSCLC present with advanced stage disease not amenable to surgical resection, so only diagnostic cytology or small biopsy tumour samples are available for molecular analysis. Tere is evidence that cytology and small biopsy specimens have equivalent capacity to accurately subtype NSCLC [3]. Use of immunohistochemistry has become routine for distinction of NSCLC subtypes in cytology (and small biopsy) samples where morphology alone is insufcient [2] and in one study immunohistochemistry was less frequently required in cytology compared to small biopsy samples [3]. ALK Rearrangements in Lung Cancer Identifcation of driver mutations has become essential in lung cancer for selection of patients likely to respond to targeted therapies. A small proportion of lung adenocarcinomas harbour activating ALK (anaplastic lymphoma kinase) gene rearrangements and these tumours are highly responsive to targeted tyrosine kinase inhibitors (TKIs) such as crizotinib [4]. Te ALK gene is located on the short arm of chromosome 2 and encodes a receptor tyrosine kinase that belongs to the insulin receptor family [5]. Activation of ALK most commonly results from a small chromosomal inversion (with or without a small deletion) resulting in fusion of the intracellular kinase domain of ALK with the amino terminal end of echinoderm microtubule associated protein-like 4 (EML4) [6-8]. Diferent variants of EML4-ALK result from difering lengths of the EML4 gene being incorporated into the fusion gene [6,9,10]. More rarely, diferent partner genes fuse with ALK including KIF5B (kinesin family member 5b), TFG (TRK-fused gene) and KLC-1(kinesin light chain1) [11,12].Te various ALK fusion genes encode a constitutively activated tyrosine kinase [7,11] that stimulates cell proliferation, survival and migration mediated through RAS/RAF/MAPK1, PI3K/ AKT and JAK3-STAT3 signalling pathways [10,13]. Mouse models expressing EML4-ALK develop multiple lung adenocarcinomas that are susceptible to pharmacologic ALK inhibition [14]. Studies from unselected Western populations mostly report ALK rearrangements in about 4% of NSCLC [5]. We found ALK rearrangements in 1% of lung adenocarcinomas in an Australian multicenter study [15]. Te clinicopathological features associated with ALK rearrangements are similar to the profle associated with EGFR mutations. ALK rearrangements are associated with younger patient age and never-smokers or light smokers [6,15-19], however, racial and gender associations are less pronounced for ALK. In NSCLC, ALK rearrangements occur almost exclusively in Journal of Cytology & Histology J o u r n a l o f C y t o l o g y & H i s t o l o g y ISSN: 2157-7099