NPM‐ALK permits the survival of thymic T cells with aberrant T cell receptor rearrangements enabling thymic escape and tumor development

We present evidence to support a new model of Anaplastic Large Cell Lymphoma (ALCL) pathogenesis in which the malignancy is initiated in early thymocytes, prior to TCR rearrangement which is bypassed in NPM‐ALK transgenic mice following Notch1 expression. In support, we show that T cell receptor (TCR) rearrangements are aberrant in some human ALCL, yielding events that would not normally be permissive for survival during T cell development. However, a TCR is required for thymic egress and subsequent development of peripheral tumors in mice yet this TCR must be down‐regulated for T‐cell lymphomagenesis. Children affected by ALCL may thus harbor lymphoma-initiating cells in the thymocyte population that seeds relapse after chemotherapy. comparative genomic hybridization data from 43 human Anaplastic Large Cell Lymphoma (ALCL) samples and control samples