Clinicopathological Analyses of Solitary Plasmacytoma in a Single Institution of China

Background: Solitary plasmacytoma (SP), accounting for less than 5% of all plasma cell dyscrasias, is a rare disorder with localized proliferation of neoplastic monoclonal plasma cell. Due to the rarity of SP, further understanding of the spectrum of clinicopathologic features is needed. Methods: A 5-year retrospective analysis of cases from a single institution was conducted. Specifically, clinical characteristics of all SP patients were collected, and quantitative immunohistochemical analysis on tissue microarray was performed. Findings: Thirteen cases were identified from our pathology archives, with solitary plasmacytoma of bone (SPB) accounting for 30.8% and extraosseous plasmacytoma (EP) for 69.2% of the cases. The mean age of EP is one decade older than SPB. No gender disparity is identified. The most common sites involved are the vertebrae and nasopharynx. Histologically, the tumors consist of plasmacytoid cells diffusely infiltrating the involved tissue, and can be classified into two grades based on the degree of differentiation. Immunohistochemically the tumor cells are positive for CD38, CD138, MUM-1, and exhibit light chain restriction. Ki-67 proliferation index averages at 30%. Quantitative immunohistochemistry stain analysis showed the neoplastic cells exhibiting decreased CD38 in integrated optical density (IOD). Epstein-Barr virus-encoded small RNAs (EBER) was negative in all six cases tested. Two cases were positive for IgH gene rearrangement. Interpretation: SP is a rare plasmacytoid tumor that occurs more frequently in older patients. Diagnosis requires a systematic approach, combined with the pathological characteristics of plasmacytoid morphology, immunophenotype and the light chain restriction. Furthermore In our study the data shows that the cases of EP is more than SPB, Which is opposite from the litterature. Further studies with more patients and long-time follow-up may provide more information to understand risk of recurrence and progression from SP to multiple myeloma (MM). Funding: Department of Science and Technology, Hubei Provincial People's Government (2020CFB343). Declaration of Interest: None to declare. Ethical Approval: This study was approved by the Ethics Committee of Zhongnan Hospital for discarded diagnostic material (no consent required).