ALK Gene Rearrangements: A New Therapeutic Target in a Molecularly Defined Subset of Non-small Cell Lung Cancer

Transforming rearrangements of the ALK (anaplastic lymphoma kinase) gene have recently been described in non-small cell lung cancer (NSCLC). The most common rearrangement arises from an inversion in the short arm of chromosome 2 that creates a fusion between the 5′ portion of the EML4 (echinoderm microtubule-associated protein-like 4) gene and the 3′ portion of the ALK gene. At least seven ALK gene rearrangement variants have been described involving different EML4-ALK breakpoints or rarely other non-EML4 fusion partners. ALK rearrangements may be readily identified in tumor tissue by reverse transcription-polymerase chain reaction or fluorescent in situ hybridization. Although ALK gene rearrangements affect only about 4% of all lung cancers, they are more frequent in adenocarcinomas, in never or light smokers, and seem almost mutually exclusive with activating EGFR or KRAS mutations. Promising results seen in patients with NSCLC containing fluorescent in situ hybridization-detected ALK rearrangements treated on a phase I study with PF02341066, an oral ALK inhibitor, indicate that ALK represents a new therapeutic target in this molecularly defined subset of NSCLC.