LAUSR

A 17yearold male patient had been diagnosed 10 months previously with acute monocytic leukaemia, corresponding to AMLM5 according to FrenchAmericanBritish (FAB) categorisation, with KMT2A::MLLT10. After induction and consolidation chemotherapy, he achieved a complete remission (CR). Unfortunately, he relapsed after only 3 months. A bone marrow (BM) aspirate showed 89% round or oval blast cells with regular nuclei, agranular and moderately blue to grey cytoplasm, delicate lacy chromatin and prominent nucleoli (top images, ×100 objective). Immunophenotyping showed the blasts to be positive for CD34, CD33, CD13, HLADR, CD64, CD11c, CD38, CD123, CD4 (weak), CD7 (weak), CD56 (partial) and CD15 (partial), indicating monocytic differentiation. Conventional cytogenetic analysis showed 46,XY. All the evidence indicated a relapse of AMLM5. In view of the early relapse and lack of response to DCA (decitabine+cytarabine+aclarubicin) plus venetoclax, salvage allogeneic haematopoietic stem cell transplantation was performed. Nevertheless, a BM reexamination performed two months later showed 21% blasts with round, slightly irregular, or indented nuclei with fine reticular chromatin and 1– 3 nucleoli. The abundant cytoplasm was basophilic and agranular, with distinct blebs or pseudopod formation (bottom images). Flow cytometry demonstrated expression of CD33 (weak), CD42a, CD42b and CD61, with no expression of CD19, CD22, CD34, CD117, CD36, myeloperoxidase, CD11b or CD13, indicating megakaryocyte lineage (FAB classification, AML M7). KMT2A::MLLT10 was demonstrated by quantitative realtime polymerase chain reaction. The clinical course and investigations thus indicated transformation of KMT2Arearranged acute monocytic leukaemia to acute megakaryoblastic leukaemia. Of note, translocation with an 11q23 breakpoint was not observed during the course of the illness. Very few cases of AMLM7 with KMT2A::MLLT10 have been described. Of interest, this case was not a de novo AMLM7 with KMT2Arearrangement, but a particularly uncommon transformation from relapsed AMLM5. The knowledge of the fusion partner in KMT2Arearranged AML is clinically relevant as prognosis varies depending on the fusion partner. Molecular studies may be needed to identify KMT2A involvement and its fusion partner.