One of the most challenging issues in oncology research and treatment is 
identifying oncogenic drivers within an individual patient's tumor which can be 
directly targeted by a clinically available therapeutic drug. In this context, 
gene fusions as one important example of genetic aberrations leading to 
carcinogenesis follow the widely accepted concept that cell growth and 
proliferation are driven by the accomplished fusion (usually involving former 
proto-oncogenes) and may therefore be successfully inhibited by substances 
directed against the fusion. This concept has already been established with 
oncogenic gene fusions like BCR-ABL in chronic myelogenous leukemia (CML) or 
anaplastic lymphoma kinase (ALK) in lung cancer, including special tyrosine 
kinase inhibitors (TKIs) which are able to block the activation of the depending 
downstream proliferation pathways and, consequently, tumor growth. During the 
last decade, the NTRK1, 2, and 3 genes, encoding the TRKA, B, and C proteins, 
have attracted increasing attention as another significant and targetable gene 
fusion in a variety of cancers. Several TRK inhibitors have been developed, and 
one of them, Larotrectinib (formerly known as LOXO-101), represents an orally 
available, selective inhibitor of the TRK receptor family that has already shown 
substantial clinical benefit in both pediatric and adult patients harboring an 
NTRK gene fusion over the last few years.