ALK and anaplastic large cell lymphoma: This is a TCR profile that is not consistent with normal thymocyte development but is consistent with observations made by ourselves and others that ALCL very rarely express the TCRβ protein by immunohistochemistry [86,96] and, more specifically, with our observation that NPM-ALK can replace the TCRβ signalling cascade in mice (CD4/NPM-ALK/RAG−/− mice produce thymic lymphomas that appear to be mature, post TCR-rearrangement thymocytes) [53,97].