NTRK-Fusions - A new kid on the block.

The neurotrophic tyrosine receptor kinases (NTRK) play an important role in the development and function of the nervous system. Fusions involving NTRK and a wide range of genes that act as fusion partners are oncogenic and activate well-known signal transduction pathways like the MAPK-ERK pathway. NTRK fusions occur in many very different tumor entities in children and youth as well as in adults. There are a few tumors like secretory breast cancer and congenital fibrosarcoma for which NTRK fusions are pathognomonic. At the same time there a large number of tumors in which NTRK fusions occur in very rare frequency (e.g., lung cancer). TRK inhibitors offer now the possibility to use NTRK fusion as antitumorigenic targets in a tumor agnostic fashion regardless of the basic histology. It is the task of modern pathology to identify such targetable fusions in a highly effective and efficient manner.