The ALK gene encodes a receptor tyrosine kinase, which belongs to the insulin receptor superfamily. It plays an important role in the development of the brain and exerts its effects on specific neurons in the nervous system. This gene has been found to be rearranged, mutated, or amplified in a series of tumors including anaplastic large cell lymphomas, neuroblastoma, and non-small cell lung cancer. The chromosomal rearrangements are the most common genetic alterations in this gene, which result in creation of multiple fusion genes in tumorigenesis, including ALK//EML4, ALK/RANBP2, ALK/ATIC, ALK/TFG, ALK/NPM1, ALK/SQSTM1, ALK/KIF5B, ALK/CLTC, ALK/TPM4, and ALK/MSN. The specificity of the anti-human ALK antibody (clone 1A4)was established on known ALK positive and negative non-small cell carcinoma (NSCLC). The anti-ALK presented no staining on formalin fixed ALK negative NSCLC tissue and positive staining on FFPE ALK positive NSCLC tissue using immunohistochemistry.