The RET (10q11.21) Break Apart FISH probe is a dual color probe, designed to detect chromosomal rearrangements involving the RET proto-oncogene (10q11.21). The RET proto-oncogene encodes a tyrosine kinase receptor and under normal conditions, it functions as a signaling molecule involved in cellular growth and differentiation. Chromosomal rearrangements involving RET were initially identified in papillary thyroid carcinoma (1). However, RET gene rearrangements have been identified in Non-Small-Cell Lung Cancer (NSCLC) patients (2). RET gene rearrangements in NSCLC result in a novel gene fusion event involving RET and KIF5B gene (3). This genetic aberration is believed to play a role in oncogenesis in NSCLC (3). RET gene rearrangements can be identified using Fluorescence in situ Hybridization (FISH).