Abstract:

Aim: Current guidelines recommend evaluating the expression of PD-L1 immunohistochemically in most tumors, especially lung cancer. However, it is not easy to evaluate the immunohistochemical staining of PD-L1 because of the tumor heterogeneity. Therefore, we aim to evaluate the different patterns of PD-L1 in the lung’s nonsmall cell carcinoma and the relationship with clinicopathological features. We also wanted to see if cell blocks obtained from cytology materials can be an alternative for PD-L1 immunohistochemistry. Material and Method: We retrospectively analyzed the immunohistochemical patterns of PD-L1 performed between 2018 and 2019. Biopsy/aspiration procedure of tumors, tumor type, patient’s age, and gender were reviewed. Positive tumor cells (percentage) were categorized according to density and distribution as negative (<1%), low expression (1–49%), and high expression (>50%). Results: Material adequacy was found to be satisfactory in evaluating PD-L1 in the cases of cell blocks. Positive staining with PDL1 was detected even with a small number of tumor cells in the cell block. For optimal evaluation of PD-L1 expression in the cell block, the tumor cell ratio of 10% is significant (p=0.002). The cases with negative PD-L1 expression mostly belonged to small biopsy samples (48.3%). However, the difference in PD-L1 expression in histological and cytological samples was insignificant (p=0.79). Besides this, expression of PD-L1 was negative in almost half of the cases (48.3%) diagnosed with squamous cell carcinoma. In adenocarcinoma cases, the PD-L1 expression rate was between 1–49 % in more than half (51.8%) of them. The difference in histological subtype was not significant in PD-L1 staining (p=0.009). Conclusion: In conclusion, we can use cell blocks for immunohistochemical evaluation of PD-L1 expression. Analysis of PD-L1 staining in cytological and histological tissue samples may be a guide for other studies.

Keywords: