In patients with a clinically normal immune function, the Epstein-Barr virus is predominantly negative, and the mutation frequency of proto-oncogenes, including Pim-1, RhoH/TTF and c-Myc, is two to five-fold higher than in patients with extracranial diffuse large B-cell lymphomas (1). The gene discussed is PIM1; the disease is diffuse large B-cell lymphoma.