Granular B‐lineage acute lymphoblastic leukaemia mimicking acute myeloid leukaemia

A 65-year-old female presented with 2 months of progressive weakness and dizziness. Physical examination was unremarkable except for pallor. A full blood count showed haemoglobin concentration 59 g/l, leucocyte count 2·69 × 109/l and platelet count 86 × 109/l. A bone marrow aspirate showed hypercellularity with 91% blast cells. These cells had large, variably irregular nuclei with one to four nucleoli and abundant cytoplasm; 75% of them had numerous cytoplasmic granules, but no Auer rods (top left). The blast cells were negative for myeloperoxidase (MPO) (top right), but positive on periodic acid–Schiff staining (bottom left). Double-esterase double-staining showed weak focal positivity for α-naphthol acetate esterase without inhibition by fluoride and negativity for naphthol AS-D chloroacetate esterase (bottom right). By flow cytometry the blasts were positive for CD19, CD79a, CD34, CD33, CD10 and CD13, and negative for cytoplasmic (c) μ chain, CD2, HLA-DR, CD7, CD117, CD14, CD15, CD16, CD56, CD64, cCD3 and cMPO. A diagnosis of granular B-lineage acute lymphoblastic leukaemia (B-ALL) was made. One of the main morphological features that distinguishes acute myeloid leukaemia from ALL is the presence of cytoplasmic granules in blast cells, which are usually lacking in ALL. However, ALL may present with significant numbers of cytoplasmic granules in blast cells (so-called granular ALL); this usually occurs in children (2–7%) although extremely rare adult cases have been reported (Pitman & Qin, 2007). This case demonstrates that morphology can be very confusing, so that immunophenotyping is of critical importance in acute leukaemia, both at presentation and relapse.