Sibling donor-derived myeloid sarcoma after hematopoietic stem cell transplant

Donor-derived myeloid sarcoma (DDMS) is a rare complication which occurs when donor stem cells undergo leukemic transformation. We report here two cases of DDMS following successful allogenic hematopoietic stem cell transplant (allo-HSCT) from HLA-identical, sex-mismatched sibling donors. Both were males in their fourth decade of life and originally diagnosed in 2012 with acute myeloid leukemia (AML) with t(6;11)(q27;q23) and AML with myelodysplasia-related changes (AML-MRC), respectively. They went onto allo-HSCT from their respective haploidentical sisters as donors and achieved complete engraftment in 2014. Both were in remission until 2019 when they were diagnosed with clinical relapse of AML in the setting of DDMS, one presenting in bilateral tibiae and the other in the testis. Verifying donor origin in AML relapse is critical as transformed donor cells may have different genetic alterations and behaviors from initial AML. We reviewed the literature of donor derived myeloid sarcoma and discussed the pathogenesis of this rare late complication of HSCT.