The ALK gene is located on chromosome 2p23.2. The ALK Break Apart FISH probe is designed to label both ends of the ALK gene, respectively. A 600 Kb orange probe is designed at the 3′ end of the ALK gene, and a 800 Kb green probe is designed at the 5′ end of the ALK gene.

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase which was discovered in anaplastic large-cell lymphoma (ALCL). In non-small cell lung cancer, the inv(2)(p21;p23) forms the fusion gene EML4-ALK, which represents a molecular subtype of NSCLC.