Background: The concurrent presentation of non-Hodgkin lymphoma and multiple myeloma is a very rare condition and only few cases have been reported. Case Presentation: In this case report, we discuss a patient who presented with abdominal pain, weight loss, and melena. After the patient’s admission, several examinations were conducted. Microscopic findings in pathological studies and immunohistochemistry staining studies revealed a malignant non-Hodgkin B-cell lymphoma. A monoclonal free light chain protein was documented in the urine protein electrophoresis. Serum protein electrophoresis was reported to be normal. Bone marrow biopsy demonstrated cellularity plasma cell aggregations as multiple myeloma. Small bowel segmental resection surgery was the treatment plan. To prevent the relapse of chemotherapy, rituximab in combination with cyclophosphamide, doxorubicin, vincristine, and prednisone chemotherapy was tolerated by the patient. Finally, melena did not last after the resection and hemoglobin returned to its normal range. Conclusion: In conclusion, this case report suggests that both multiple myeloma and non-Hodgkin’s lymphoma are hematopoietic malignancies which originate from B-cell lymphocytes. To understand, properly manage, and treat this rare condition, multiple studies are required, and this can be achieved by comparing similar cases.

Keywords: Non-Hodgkin lymphoma, multiple myeloma, proliferative disease, malignancy, electrophoresis