PRDM1 and aggressive NK-cell leukemia: However, bona fide tumour suppressor activity has been demonstrated for PRDM1 (BLIMP1) in diffuse large B-cell lymphomas, natural killer cell leukaemia/lymphoma and systemic anaplastic large cell lymphoma, where homozygous inactivation, through mutation unmasked by 6q deletion, has been demonstrated [6–8].