NGF and neuroblastoma: Another RTK involved in NB is tropomyosin receptor kinase (TRK)A.20 High TRKA expression is a favorable marker,20 whereas high expression of the related TRKB is a marker of poor prognosis and progression in NB.21 Alternative splicing adds further complexity: a truncated TRKB isoform is preferentially expressed in differentiating NB,22,23 whereas an isoform of TRKA that does not bind nerve growth factor is found in unfavorable NB.24