Donor cell-derived myelofibrosis relapse after allogeneic stem cell transplantation

Primary myelofibrosis (PMF) is a rare myeloproliferative neoplasm characterized by clonal proliferation of mature myeloid lineages derived from stem cells (erythrocytes, leukocytes and magakaryocytes) with variable megakaryocyte atypia associated with reticulin and / or collagen bone marrow (BM) fibrosis, osteosclerosis, ineffective erythropoiesis, angiogenesis, extramedullary hematopoiesis and abnormal expression of cytokines. Allogeneic hemopoietic stem cell transplantation (alloHSCT) is currently the only curative approach for patients with myelofibrosis, and for this reason the number of allografts for these indications have been growing over the past years. Unfortunately relapse of myelofibrosis (MF) after an alloHSCT occurs in 10-40% of cases: patients usually present with a declining donor chimerism, and a reappearance of driver mutations if present; BM biopsy is usually consistent with typical megakaryocyte abnormalities and stromal fibrosis. Ultimately BM cells exhibit progressive loss of donor chimerism, and the relapse is therefore of recipient origin. Here we report two allografted MF patients who relapsed in donor cells.