Very late relapse of plasma cell myeloma after allogeneic hematopoietic stem cell transplantation

Very late (more than 10 years) relapse of plasma cell myeloma after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is rare. The most common relapse pattern in such cases involves the bone marrow. Here, we report the case of a 51-year-old woman whose myeloma relapsed 15 years after allo-HSCT. She retained full donor chimerism, and the myeloma presented as soft tissue in the colonic wall. According to our review of the literature, this case presents the longest time to relapse after allo-HSCT. Patients with myeloma who undergo allo-HSCT should continue to receive regular follow-up even after 15 years.