ALK-rearrangements and testing methods in non-small cell lung cancer: a review

The anaplastic lymphoma tyrosine kinase (ALK) gene was first described as a driver mutation in anaplastic non-Hodgkin's lymphoma. Dysregulated ALK expression is now an identified driver mutation in nearly twenty different human malignancies, including 4-9% of non-small cell lung cancers (NSCLC). The tyrosine kinase inhibitor crizotinib is more effective than standard chemotherapeutic agents in treating ALK positive NSCLC, making molecular diagnostic testing for dysregulated ALK expression a necessary step in identifying optimal treatment modalities. Here we review ALKmediated signal transduction pathways and compare the molecular protocols used to identify dysregulated ALK expression in NSCLC. We also discuss the use of crizotinib and second generation ALK tyrosine kinase inhibitors in the treatment of ALK positive NSCLC, and the known mechanisms of crizotinib resistance in NSCLC.