Specific fusions of the NTRK gene are associated with certain tumours (e.g. the ETV6–NTRK3 fusion gene is detected in 90–100% of mammary analogue secretory carcinomas, more than 90% of secretory breast carcinomas, and most cases of infantile fibrosarcoma and congenital mesoblastic nephroma). This evidence concerns the gene NTRK3 and congenital fibrosarcoma.