Giant Retroperitoneal Plasmacytoid Neoplasm With Immunomorphologic Overlap Between Extramedullary Plasmacytoma and Plasmablastic Lymphoma: a Diagnostic and Therapeutic Challenge
Year: 2026
Type: article
Study design: Case Report
Abstract: Background Isolated extramedullary plasmacytoma (EMP) is a rare plasma cell neoplasm, accounting for 3–5% of plasma cell malignancies, with strong predilection for the head and neck region. Retroperitoneal presentation is exceptional, and histopathological distinction from plasmablastic lymphoma (PBL) — an aggressive differential requiring a markedly different treatment approach — remains a recognized diagnostic challenge in hematopathology. Case report A 43-year-old man presented with a one-year history of progressive limb edema and abdominal distension. Diagnostic biopsy was delayed seven months by public health system wait times, during which the tumor progressed to a giant retroperitoneal mass (15.6 × 18.1 × 21.7 cm), causing bilateral hydroureteronephrosis with KDIGO stage 3 post-renal acute kidney injury requiring first-time hemodialysis, bilateral ureteral stenting/nephrostomy, deep vein thrombosis requiring inferior vena cava filter placement (pulmonary embolism was ruled out), and a postoperative enterocutaneous fistula complicated by a frozen abdomen. Initial biopsy showed monoclonal, lambda-restricted plasma cell proliferation; an expanded immunohistochemical panel later revealed a Ki-67 index of ∼95% and c-Myc positivity in 60% of cells, alongside absence of B-lineage markers and HHV-8 — findings favoring EMP but insufficient to definitively exclude PBL, as EBER-ISH and MYC FISH could not be performed due to resource constraints. Bone marrow flow cytometry showed no clonal plasma cell population, and whole-body CT showed no lytic lesions. The frozen abdomen precluded both fistula repair and radiotherapy. In accordance with the patient's wishes, intensive chemotherapy was declined; he received biweekly bortezomib-dexamethasone but died from progressive surgical-obstructive complications. Conclusion This case illustrates a rare, giant retroperitoneal presentation of EMP in which cascading mechanical complications — compounded by diagnostic delay within a resource-constrained health system — foreclosed definitive local therapy despite active systemic treatment. It further documents, through a complete immunohistochemical workup, the recognized diagnostic gray zone between EMP and PBL, highlighting real-world limitations in achieving diagnostic certainty when confirmatory molecular testing is unavailable.
Institution: Hospital Santa Izabel
Language: English
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W7223087848