Do Not Judge a Book by Its Cover! When a B‐All Pretended to Be a <scp>CLL</scp>

A 45-year-old man was admitted with B symptoms and pancytopenia. Peripheral blood smear analysis demonstrated numerous small lymphoid cells with occasional blasts and moderate myelemia. Bone marrow aspiration showed a marked infiltration by lymphoid cells (97%) morphologically consistent with chronic lymphocytic leukaemia. However, flow cytometry ultimately confirmed the diagnosis of B-cell acute lymphoblastic leukaemia. Molecular testing revealed a missense mutation in exon 10 of the ZEB2 gene (p.H1038R). The patient received treatment according to the GRAALL 2024, in combination with rituximab. Chemoresistance was observed at day 8, leading to an allogeneic haematopoietic stem cell transplant. This observation illustrates the diagnostic difficulty raised by unusual morphologic variants of acute lymphoblastic leukaemia.