113 Background: OSCC is a public health problem worldwide, mainly due to its advanced stage diagnosis. The late diagnosis is a nonsense problem in view of this neoplasia often begins as PML. Clinical, molecular and immunological factors have been associated with the cancerization process. Objective: evaluate clinical differences and immunohistochemistry expression of PD1, CD4 and CD8 in PML that transformed in OSCC (PML-OSCC) and PML that didn´t transformed in OSCC (PML-NOSSC). Methods: CD4, CD8 and PD1 immunohistochemistry studies were carried out on PML and OSCC samples of 11 patients with PML – OSCC and PML samples of 14 patients with PML-NOSCC. Statistical differences were analyzed between the two groups: PML-OSCC and PML-NOSCC. Results: Non-homogenous leukoplakia, tongue and lack of exposure to tobacco were associated with cancerization. PD1 strong immunoexpression were observed in 63.6% of PML and 90.9% of OSCC. There was no statistical difference CD4+ cells level in PML-OSCC and PML-NOSCC. A significant increase in CD8+ cells was noted in OSCC comparing with PML–OSCC (p = 0.05). CD8+ cells levels is higher in PML-NOSCC compared with PML-OSCC (p = 0.027). Conclusions: CD8+ cells infiltrate more PML-NOSCC than PML-OSCC. Carcinoma is more infiltrated by CD8+ cells than its associated premalignant lesion. The evolution of immune response from an immunosurveillance phase to editing, equilibrium, suppression and immuno-escape can be present in oral carcinogenesis process. Research Funding: FAPEMIG (Minas Gerais State Research Foundation).

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