119 Plasmablastic lymphoma in an adult with monogenic Crohn’s disease and biallelic STXBP2 mutation

Introduction/Objective Plasmablastic lymphoma (PBL) is an aggressive large B-cell neoplasm with a terminal B-cell differentiation phenotype that typically arises in immunocompromised patients. In the current literature, a majority of cases involve concurrent HIV infection, while fewer cases discuss other causes of immunodeficiency. This case features a patient with a germline mutation who ultimately developed a PBL. Methods/Case Report A 41-year-old male with a biallelic STXBP2 mutation resulting in hypogammaglobulinemia and monogenic Crohn’s disease, treated with extensive immunotherapy, presented with hemorrhagic ostomy pouch contents. A colonoscopy revealed a partially obstructing mass. Biopsies and subsequent proctocolectomy sections demonstrated sheets of large, pleomorphic, plasmacytoid cells with vesicular nuclei and prominent nucleoli. These cells were positive for CD3, CD138, MUM-1, and EBER, but negative for CD20, PAX-5, CD34, CD117, and HHV8. The Ki67 proliferative index was high. These findings were consistent with an EBV-positive plasmablastic lymphoma. Results NA Conclusion This study highlights a case of PBL in an HIV-negative patient with both acquired and inborn errors of immunity. While STXBP2 mutations are historically associated with hemophagocytic lymphohistiocytosis, minimal case reports describe a connection with lymphomas. With the progressive advancements in molecular sequencing, additional research is necessary to elucidate the relationship between this hereditary mutation and subsequent development of hematologic malignancies.