Dense Plasma Cell Infiltrates Foster Stromal Desmoplasia and Immune Evasion in Oral Squamous Cell Carcinoma

Background/Objectives: The interaction between malignant cells and the extracellular matrix (ECM) is a critical driver of tumor invasion. ECM remodeling and desmoplasia characterize the tumor microenvironment, facilitating both stromal fibrosis and malignant progression. This study was conducted to evaluate plasma cell infiltration across distinct stromal patterns in oral squamous cell carcinoma (OSCC) and investigate its association with stromal desmoplasia and immune evasion. Methods: A total of eighty-seven cases that were histopathologically diagnosed as OSCC were included in the study. Immunohistochemical staining for IgG4, CD138, VEGF, TGF-β 1, and CD31 was performed on deparaffinized tissue sections, and the plasma cell count was determined. Results: Distinct stromal architectural patterns were observed across different grades of OSCC. Stromal desmoplasia initiated with inflammatory cell infiltration into the stroma at an early stage, followed by infiltration of the dense collagenous stroma; both revealed dense plasma cell infiltrates. However, the difference in plasma cell density between OSCC grades was not shown to be statistically significant using the chi-square test and ANOVA (p = 0.761 and p = 0.152, respectively). Conclusions: Stromal desmoplasia and immune evasion are associated with dense plasma cell infiltration, suggesting that these cells may serve as a potential prognostic indicator of the invasive progression in OSCC.