Approximately 3–7% of lung tumors harbor ALK fusions (Koivunen et al. 2008; Kwak et al. 2010; Shinmura et al. 2008; Soda et al. 2007; Takeuchi et al. 2008; Wong et al. 2009). ALK fusions are more commonly found in light smokers (< 10 pack years) and/or never-smokers (Inamura et al. 2009; Koivunen et al. 2008; Kwak et al. 2010; Soda et al. 2007; Wong et al. 2009). ALK fusions are also associated with younger age (Inamura et al. 2009; Kwak et al. 2010; Wong et al. 2009) and adenocarcinomas with acinar histology (Inamura et al. 2009; Wong et al. 2009) or signet-ring cells (Kwak et al. 2010). Clinically, the presence of EML4-ALK fusions is associated with EGFR tyrosine kinase inhibitor (TKI) resistance (Shaw et al. 2009).

Multiple different ALK rearrangements have been described in NSCLC. The majority of these ALK fusion variants are comprised of portions of the echinoderm microtubule-associated protein-like 4 (EML4) gene with the ALK gene. At least nine different EML4-ALK fusion variants have been identified in NSCLC (Figure 1; Choi et al. 2008; Horn and Pao 2009; Koivunen et al. 2008; Soda et al. 2007; Takeuchi et al. 2008; Takeuchi et al. 2009; Wong et al. 2009). In addition, non-EML4 fusion partners have also been identified, including KIF5B-ALK (Takeuchi et al. 2009) and TFG-ALK (Rikova et al. 2007). Clinically, the presence of an ALK rearrangement is detected by fluorescence in situ hybridization (FISH) with an ALK break apart probe. FISH testing is not able to discern which particular ALK fusion is found in a clinical sample.

1. WB of EML4-ALK V3b/BaF3 expression

Figure 1. WB of ALK expression