Blastoid transformation of MCL is usually associated with <i>TP53</i> mutations, homozygous deletions of <i>CDKN2A</i> and <i>CDKN2C</i>, amplifications and overexpression of <i>CDK4</i>,<i> </i>and occasionally microdeletions of <i>RB1</i>, and is associated with an aggressive disease course. This evidence concerns the gene RB1 and mantle cell lymphoma.