Genotypic ITH using FISH to identify receptor tyrosine kinase (RTK) amplifications in archivalglioblastoma (GBM) samples. Mosaic amplification of up to three different RTKs was observedin cells of the same tumour in a mutually exclusive fashion, indicating coexisting subpopulations.These cells shared other genetic events inTP53 orCDKN2A, signifying that they originated fromthe same precursor. Here, NTRK1 is linked to glioblastoma.