The anaplastic lymphoma kinase (ALK) has emerged as a potentially relevant biomarker and therapeutic target in a variety of solid and hematologic malignancies. It is a receptor tyrosine kinase (RTK) that is known to be activated either by point mutations or by chromosomal translocations. These genetic alterations act as oncogenic drivers and promote constitutive, ligand-independent activation of this RTK. Approximately 3–7% of non-small cell lung cancers (NSCLC) harbor ALK fusions/rearrangements. This fusion oncogene rearrangement is transforming both in vitro and in vivo and defines a distinct clinicopathologic subset of NSCLC that are highly sensitive to therapy with ALK-targeted inhibitors. While crizotinib is highly active in patients with ALK-positive NSCLC, patients have been shown to invariably develop resistance to this drug. In approximately one-third of resistant cases, tumors can acquire a secondary mutation within the ALK tyrosine kinase domain. ALK F1174 variant is a somatic mutation in the ALK kinase domain and has been detected in neuroblastomas. It has a transforming activity in vitro and in vivo, and may cause resistance to crizotinib as well as second generation ALK inhibitors such as ceritinib.