Abstract
Background/Objectives: Tumor-infiltrating lymphocytes (TILs) play a crucial role in the tumor microenvironment (TME), influencing the progression, prognosis, and response to treatment in oral squamous cell carcinoma (OSCC) and its precursors, oral potentially malignant disorders (OPMDs). This scoping review assesses the current literature on TILs in the TME of OSCC and OPMDs, aiming to identify trends and gaps in the research. Methods: A comprehensive search was performed in PubMed, using the following query terms: "Tumor Microenvironment AND (mouth neoplasms OR oral lichen OR leukoplakia OR oral lichenoid OR dysplasia OR GVHD OR lupus)". Based on the inclusion criteria, we selected in vivo human original research and clinical observational studies that focused on TILs within the TME of OSCC and OPMDs. Results: Out of 1152 results in PubMed, 58 studies were selected and analyzed. These studies investigated various TILs, including T cells, B cells, and natural killer (NK) cells. Of these, 47 studies focused on the OSCC TME, 4 examined the OPMDs ME, and 7 compared OSCC TME and OPMDs ME. Discussion: While TILs in OSCC have been extensively studied, research on infiltrating lymphocytes in OPMDs is still limited. In OSCC, CD8+ T cells, T helper 1 cells, and NK cells are associated with strong antitumor activity, whereas CD4+ T cells, including T helper 2 and regulatory T cells, are linked to protumoral effects. B cells remain less explored due to their low frequency in the TME. In OPMDs, trends suggest an increase in activated CD8+ T cells in OLP and lower NK cell numbers compared to OSCC, which may contribute to malignant transformation. Understanding the spatial distribution and activation status of TILs within the TME is essential for deciphering their role. The variability in TIL composition highlights the complexity of the TME. Conclusions: Current knowledge remains preliminary, though it highlights the crucial role of TILs in carcinogenesis and OSCC. A more in-depth understanding could improve diagnostic and therapeutic strategies, including the assessment of the risk of malignant transformation in OPMDs.