The discovery of chromosomal rearrangements involving the anaplastic lymphoma kinase (ALK) gene in non-small cell lung cancer (NSCLC) has stimulated renewed interest in oncogenic fusions as potential therapeutic targets. Recently, genetic alterations in ROS1 and RET were identified in patients with NSCLC. Like ALK, genetic alterations in ROS1 and RET involve chromosomal rearrangements that result in the formation of chimeric fusion kinases capable of oncogenic transformation. Notably, ROS1 and RET rearrangements are rarely found with other genetic alterations, such as EGFR, KRAS, or ALK. This finding suggests that both ROS1 and RET are independent oncogenic drivers that may be viable therapeutic targets. In initial screening studies, ROS1 and RET rearrangements were identified at similar frequencies (approximately 1%-2%), using a variety of genotyping techniques. Importantly, patients with either ROS1 or RET rearrangements appear to have unique clinical and pathologic features that may facilitate identification and enrichment strategies. These features may in turn expedite enrollment in clinical trials evaluating genotype-directed therapies in these rare patient populations. In this review, we summarize the molecular biology, clinical features, detection, and targeting of ROS1 and RET rearrangements in NSCLC. The Oncologist 2013;18:865-875 Implications for Practice: Treatment approaches for non-small cell lung cancer (NSCLC) have been advanced in recent years by the identification of distinct, molecularly-defined subsets of patients that derive benefit from targeted therapies. As a result, the field has placed greater focus on identifying new molecular targets. Recently, ROS1 and RET fusions were independently identified in 1%-2% of patients with NSCLC. Preclinical data and early clinical findings suggest that both may be viable therapeutic targets. In this review, we summarize this data as well as the clinical and pathologic features associated with these fusions. This may in turn inform screening strategies and the development of clinical trials evaluating genotype-driven therapies in these patient populations.
INTRODUCTIONThe 2004 discovery that somatic mutations in the epidermal growth factor receptor (EGFR) confer sensitivity to EGFR tyrosine kinase inhibitors (TKIs) established a new treatment paradigm in non-small cell lung cancer (NSCLC) [1][2][3]. This discovery also placed greater focus on identifying new molecular subsets of NSCLC that may benefit from targeted therapies. In particular, emphasis has been placed on finding new "driver" oncogenes, so named because these genes are central to the growth and viability of cancer cells (e.g., mutant KRAS, BRAF, or HER2). Until recently, genetic alterations in NSCLC driver oncogenes were presumed to occur predominantly through point mutations or small insertions or deletions. Chromosomal translocations were thought to be infrequent events in solid tumors [4,5]. In 2007, however, Soda and colleagues discovered a novel fusion gene generated by a chromos...