Background: Extramedullary plasmacytoma of the retroperitoneum is rare. Furthermore, plasmacytoma with anaplastic features can be confused with high grade sarcoma clinically and histologically, particularly when the initial immunohistochemical tumor markers are negative. However, paying attention to cytologic imprint smears can give valuable clues to the correct diagnosis.
Case: A 73-year-old male was admitted to our hospital with a recent history of back pain. Abdominal computed tomography revealed a large retroperitoneal mass (6.8 x 5.1 cm). The initial pathologic evaluation revealed a high grade pleomorphic neoplasm that failed to express multiple epithelial, mesenchymal, lymphoid and melanoma immunohistochemical markers. Subsequent fresh tissue evaluation with touch imprints and immunophenotypic characterization confirmed the plasma cell origin of the tumor. Thorough retrospective review of the touch imprint smears clearly showed the plasmacytic cytologic features. Features of multiple myeloma were essentially absent.
Conclusion: Performing cytologic imprint smears on fresh tissue material may help in making the correct diagnosis and is highly recommended.