In this study, we found that (1) MYCT1 is located in one of the three smallest overlapping regions of diffuse large B-cell lymphoma; (2) MYCT1 alters the chromosomal instability of diffuse large B-cell lymphoma cells; (3) MYCT1 is negatively correlated with RUNX1 in lymphoma patients and MYCT1 represses RUNX1 transcription by binding MAX in diffuse large B-cell lymphoma cells; and (4) MYCT1 inhibits proliferation in diffuse large B-cell lymphoma probably by suppressing RUNX1 transcription. The gene discussed is RUNX1; the disease is diffuse large B-cell lymphoma.