The bone marrow biopsy (day 44) disclosed: (a) interstitial monoclonal B lymphocytosis around 10% with a CLL-like immunophenotype: PAX5+, CD5+, CD19+, CD20+; chromosome 12 trisomy; absence of TP53 mutation; unmutated immunoglobulin heavy chain variable gene, IGHV (IGHV 3–30/ IGHD 3–3*01/ IGHJ 5*02, 0% somatic hypermutation), (b) mild pancytopenia, (c) mild polytypic plasmacytosis. This evidence concerns the gene PAX5 and B-cell chronic lymphocytic leukemia.