The RET break apart FISH probe is designed to label both ends of the RET gene at chromosome 10q11.21, respectively. A 300 kb orange probe is designed at the 3′ end of the RET gene, and a 420 kb green probe is designed at the 5′ end of the RET gene.

In non-small cell lung cancer (NSCLC), RET mutations often manifest as RET fusion genes and are observed in 1–2 % of patients with NSCLC. RET expression is low in normal lung tissue, but gene rearrangements activate the RET kinase domain, leading to high expressions in lung cancer samples. Three targeted drugs – Vandetanib, Sorafenib, and Sunitinib – inhibit the activity of multiple receptor tyrosine kinases including RET, killing cells carrying RET fusion genes.