ALK and neoplasm: As has been previously suggested in primary lymphoma of the peripheral nerve, CD56 (NCAM, neural cell adhesion molecule) expression may explain localization to the nervous system through homophilic binding of CD56+ tumour cells to CD56 on neural cells.133 It should be mentioned that ALK is weakly positive in normal glia, neurones and endothelial cells in the CNS134 but does not pose a problem in determining positivity in brain anaplastic large-cell lymphoma.132ALK is expressed in neuroblastoma and glioblastoma, but these tumours are CD30–.