Very Late-Onset Post-transplant Lymphoproliferative Disorder Presenting as Small Bowel Obstruction After Initial Remission in a Living-Donor Kidney Transplant Recipient.

Post-transplant lymphoproliferative disorder (PTLD) is a lymphoid malignancy that develops in the setting of immunosuppression after solid organ transplantation. Although the incidence of PTLD after kidney transplantation is relatively low, late-onset cases are increasingly recognized with improved long-term graft survival. Very late-onset PTLD, occurring more than 10 years after transplantation, is often Epstein-Barr virus (EBV)-negative and frequently presents as monomorphic disease such as diffuse large B-cell lymphoma (DLBCL). We report a case of very late-onset EBV-negative monomorphic PTLD occurring 19 years after ABO-compatible living-donor kidney transplantation. A 49-year-old woman with stable graft function was found to have generalized lymphadenopathy on routine imaging. Lymph node biopsy confirmed CD20-positive DLBCL. After reduction of immunosuppression, she achieved complete remission with rituximab monotherapy. However, two months later, she developed small bowel obstruction due to a newly emerged intestinal mass, and histopathology confirmed recurrent DLBCL. Despite surgical resection, disease progression was observed with a mesenteric lesion. She subsequently received cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) followed by rituximab + CHOP (R-CHOP) chemotherapy, achieving complete remission while maintaining stable allograft function. This case highlights that very late-onset PTLD may behave similarly to de novo DLBCL in immunocompetent patients. Early relapse after rituximab monotherapy should prompt consideration of lymphoma-standard chemotherapy, particularly in EBV-negative monomorphic PTLD, while carefully balancing graft preservation.