ALK and lymphoma: However, this has also led to mixed results, with CD2 promoter-driven NPM-ALK transgenic mice also producing lymphomas that appear to be of a B-cell phenotype [83], and the CD4 promoter used in the same context leading in some cases to plasmacytomas [84], suggesting that either the promoters are ‘leaky’ in the transgenic setting or NPM-ALK can alter cell-lineage differentiation.