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In T lymphocytes, the Wiskott–Aldrich Syndrome protein (WASP) and WASP-interacting-protein (WIP) regulate T cell antigen receptor (TCR) signaling, but their role in lymphoma is largely unknown. Here we show that the expression of WASP and WIP is frequently low or absent in anaplastic large cell lymphoma (ALCL) compared to other T cell lymphomas. In anaplastic lymphoma kinase–positive (ALK+) ALCL, WASP and WIP expression is regulated by ALK oncogenic activity via its downstream mediators STAT3 and C/EBP-β. ALK+ lymphomas were accelerated in WASP- and WIP-deficient mice. In the absence of WASP, active GTP-bound CDC42 was increased and the genetic deletion of one CDC42 allele was sufficient to impair lymphoma growth. WASP-deficient lymphoma showed increased mitogen-activated protein kinase (MAPK) pathway activation that could be exploited as a therapeutic vulnerability. Our findings demonstrate that WASP and WIP are tumor suppressors in T cell lymphoma and suggest that MAP-kinase kinase (MEK) inhibitors combined with ALK inhibitors could achieve a more potent therapeutic effect in ALK+ ALCL., The work has been supported by grant no. FP7 ERC-2009-StG (Proposal No. 242965—‘Lunely’) (R.C.) grant no. R01 CA196703-01 (R.C.); AIRC grant no. MFAG (C.A. and M.C.); National Research Foundation of Korea (NRF) fellowship 2016R1A6A3A03006840 (T-C.C.); Bando Giovani Ricercatori grant no. 2009-GR 1603126 (M.C.); MINECO/FEDER grant no. SAF2015–70368-R and Fundación Ramón Areces (I.M.A.); the Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health (L.D.N.); and award no. T32GM007753 from the National Institute of General Medical Sciences (S.H.C.) (the content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of General Medical Sciences or the National Institutes of Health); and in part by awards from the National Institutes of Health DP2 New Innovator award no. 1DP2CA195762-01 (C.K.); the American Cancer Society Research Scholar award no. RSG-14-051-01-DMC and the Pew-Stewart Scholars in Cancer Research Grant (C.K.); and the European Union Horizon 2020 Marie Sklodowska-Curie Innovative Training Network Grant award no. 675712 for the European Research Initiative for ALK-Related Malignancies (G.G.S., I.M., C.GP. and R.C.).

Unique and shared cytogenetic abnormalities have been documented for marginal zone lymphomas (MZLs) arising at different sites. Recently, homozygous deletions of the chromosomal band 6q23, involving the tumor necrosis factor alpha–induced protein 3 (TNFAIP3, A20) gene, a negative regulator of NF-κB, were described in ocular adnexal MZL, suggesting a role for A20 as a tumor suppressor in this disease. Here, we investigated inactivation of A20 by DNA mutations or deletions in a panel of extranodal MZL (EMZL), nodal MZL (NMZL), and splenic MZL (SMZL). Inactivating mutations encoding truncated A20 proteins were identified in 6 (19%) of 32 MZLs, including 2 (18%) of 11 EMZLs, 3 (33%) of 9 NMZLs, and 1 (8%) of 12 SMZLs. Two additional unmutated nonsplenic MZLs also showed monoallelic or biallelic A20 deletions by fluorescent in situ hybridization (FISH) and/or SNP-arrays. Thus, A20 inactivation by either somatic mutation and/or deletion represents a common genetic aberration across all MZL subtypes, which may contribute to lymphomagenesis by inducing constitutive NF-κB activation.