While there are several methods that have been used to detect ALK rearrangements in tumor tissue including immunohistochemistry, fluorescent in-situ hybridization (FISH) and reverse transcriptase polymerase chain reaction, FISH testing was used as a companion diagnostic to identify patients for the crizotinib trials [22] and has emerged as the gold standard method to identify ALK gene rearrangements and is the only FDA approved test for this purpose. Here, ALK is linked to neoplasm.