trk and ret proto‐oncogene expression in human neuroblastoma specimens: High frequency of trk expression in non‐advanced stages

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Abstract
Forty‐three fresh tumor specimens of human neuroblastoma belonging to different clinical stages were analyzed for the expression of 2 proto‐oncogenes: trk, which encodes a tyrosine‐kinase receptor for nerve growth factor (NGF) and ret, another receptor‐type tyrosine kinase whose ligand is unknown. The mRNA expression of the trk gene was detected in 67.4% of cases, with increased frequency in I, II and IVs Evans' stages and in patients with favorable prognosis according to the Shimada classification. Moreover, trk expression inversely correlated with Nmyc‐gene amplification, ret mRNA was found in 36.8% of cases and equally distributed in the different stages. In addition, ngfR (low‐affinity NGF receptor)‐gene expression was present in 9 out of 25 cases. The simultaneous presence of mRNA related to both forms of the NGF receptor, while not proving the presence of a functional receptor, indicates the existence of a sub‐set of neuroblastoma cells potentially responsive to NGF.