The fact that development of peripheral ALCL in the recombinase competent NA/OT1 mice was associated with loss of TCR transgene expression, and that induction of constitutive TCR signalling by exposure of NA/OT1 mice to ova abrogated peripheral ALCL development, suggest that TCR-induced signalling acts as a tumour-suppressive mechanism in the presence of NPM–ALK in peripheral T cells. The gene discussed is NPM1; the disease is neoplasm.