ALK and neuroblastoma: The fourth (r4) subgroup encompassed tumours characterized by Del11q and high expression of genes involved in the development of the nervous system, but showed low expression of ALK. Approximately 7-9% of sporadic NB cases show inherent ALK mutations [22,23], and ALK overexpression, both in its mutated and wild type form, is demonstrated to define a poor prognosis in NB patients [24].