RET and fibrosarcoma: S100-protein-positive cases are likely to be LPF-NT and can be confirmed by the presence of gene fusions involving the NTRK family, the RAF family, or RET. In some relapsing cases or in overly superficial biopsies, a diagnosis of infantile fibrosarcoma could also be considered and then confirmed by the presence of the ETV6–NTRK3 gene fusion [30].