Diagnostic Challenges in Post-Transplant Extranodal NK/T-Cell Lymphoma Following Haploidentical Hematopoietic Stem Cell Transplantation for Acute Myeloid Leukemia: A Case Report.

A 46-year-old man with de novo acute myeloid leukemia (AML) M1 achieved complete remission after induction therapy and received consolidation treatment. Due to intermediate-risk classification and positive minimal residual disease at 6 months after consolidation treatment, he underwent haploidentical hematopoietic stem cell transplantation (HSCT) from his son. Post-transplant, he had successful neutrophil and platelet recovery without transfusion support and experienced cytomegalovirus reactivation that was effectively managed. On day +108 post-transplant, he developed fever and diarrhea. The differential diagnosis included opportunistic infection, neoplastic infiltration, and chronic on acute gastrointestinal (GI) graft-versus-host disease, given the timeframe and clinical presentation. Further investigations, including imaging and biopsies, led to a diagnosis of extranodal NK/T-cell lymphoma (ENKL). Despite adjustments in therapy, his condition worsened, and he succumbed to GI bleeding and multiorgan failure on day +144 post-transplant. This case illustrates the rare occurrence of ENKL following haploidentical HSCT in an AML patient, highlighting the diagnostic challenges and the highly aggressive clinical course of ENKL. It reinforces the importance of vigilant post-transplant monitoring, not only for infectious and relapse-related complications but also for secondary lymphoid malignancies and unusual presentations, to enable prompt diagnosis and timely intervention.