ALK and neuroblastoma: Whereas the overexpression of MYCN resulted in the development of neuroblastomas with a penetrance of less than 20%, its coexpression with the activated ALK receptor tyrosine kinase markedly enhanced both the onset and penetrance of the disease [21] The overexpression of KrasV12 induced liver tumor with a penetrance of 28% in p53+/+ fish, which increased to 32% in p53-/- fish [31].