Secondary neuroendocrine tumor after allogeneic bone marrow transplantation

Here we report a case of aggressive neuroendocrine tumor (NET), which is an extremely rare secondary solid tumor that occurs after allogeneic hematopoietic cell transplantation (allo‐HSCT). A patient with chronic active Epstein–Barr virus infection received allo‐HSCT from an HLA‐DR two allele‐mismatched unrelated donor. Four years later, he developed NET with multiple metastases. He received thoraco‐abdominal irradiation as a conditioning regimen, and developed repeated episodes of intestinal graft‐versus‐host disease, for which he received long‐term immunosuppressive therapy. Although these factors may be potential contributing factors to the development of secondary NET, the exact pathogenesis remains unclear.