Immunohistochemical Analysis of PD-L1 in Oral Squamous cell carcinoma and its association with Clinicopathological features .A Case series of 42 cases

Abstract

With an increasing incidence worldwide, with up to 370,000 new cases per year. Although recent therapeutic opportunities have improved, OSCC is still responsible for up to 177,000 deaths annually, with a 5‐year overall survival (OS) rate of around 60%.

Despite rapid advances in treatment modalities, including chemotherapy, radiotherapy, and target therapy, surgery is still a mainstream treatment for OSCC.

Emerging cancer immunotherapy using immune checkpoint blockade (ICB) has brought about drastic changes in the field of clinical oncology.This immunotherapy is based on the different survival strategies of tumor cells , One of these potential routes of tumor escape from the action of the immune system is the expression of the PD1 ligand protein (PD-L1) by tumor cells, which induces anergy in cytotoxic CD8 lymphocytes and prevents them from attacking the tumor cells by interacting with their PD1 protein.

 Blocking the binding of PD-L1 to PD-1 via an immune checkpoint inhibitor allows T cells to destroy tumor cells .Such targeted immunotherapy can be successfully achieved through the use of monoclonal antibodies directed either against PD‐L1 or PD-1.

The expression of PD‐L1 can be evaluated on both tumor cells and immune cells with immunohistochemistry ,positive staining and the patterns of PD‐L1 immunoexpression represent one of the most important indicators for correctly selecting patients eligibility for immunotherapy.

Solid cancers are also infiltrated to varying degrees by immune cells [tumor-infiltrating lymphocytes (TILs)], and this phenomenon was suggested to be a manifestation of the host immune response against cancer cells .

Studies demonstrated a positive association of high PD-L1 expression and increased TIL frequency with longer survival, also a significant positive association between PD-L1 expression and the frequency of TILs was found.

Consistent with this possibility, PD-L1 expression has been reported to be the most important predictor of the responsiveness of various cancer types to PD-L1 or PD-1 blocking antibodies .