Immunohistochemical Expression of Programmed Death-Ligand-1 (PDL-1) in Non-Melanoma Epidermal Skin Cancer with Clinicopathological Correlation

Background: Blockade of the immune checkpoint pathway involving programmed death receptor ligand-1 (PD-L1) and programmed death-1 (PD-1) has demonstrated significant clinical efficacy across a broad spectrum of malignancies. Immunohistochemical (IHC) assessment of PD-L1 protein expression is increasingly recognized as a predictive biomarker for therapeutic response to these agents.
Aim of the study: This retrospective cross-sectional cohort study evaluated PD-L1 expression in non-melanoma skin cancers (NMSC), with a primary focus on squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Also, to evaluate the correlation between PD-L1 expression in tumor cells (TCs) and tumor-infiltrating lymphocytes (TIL) with various clinicopathological parameters in the examined cases of BCC and SCC.
Patients and Methods: sixty specimens of wedge & excision from SCC& BCC cases were collected. Paraffin blocks in excision biopsy& Tissue microarray (TMA) blocks were prepared from paraffin blocks in excision biopsy. Slides were immunostained with anti-PDL1 antibody& PDL1 expression on TC & TIL was scored using intensity & percentage separately. The intensity of PD-L1 staining was graded as follows: 0 (absent), 1 (weak), 2 (moderate), and 3 (strong). PD-L1 expression levels were determined based on the proportion of positive TCs or TILs of any staining intensity. For TCs, the categories were defined as 0 (negative), <10% positive, and >10% positive. For TILs, the classification was 0 (negative), <10% positive, and >10% positive. Statistical analysis was conducted using the SPSS software, Windows version 24 (Standard edition).
Results: Among the 60 NMSCs, 35 were BCC& 25 were SCC. In SCC, significant positive relationship was observed between PDL-1 expression on TC &TIL and many pathological risk factors as subtype, grade, thickness, depth of invasion, lymphovascular invasion (LVI), and perineural invasion (PNI), but no significant correlation was observed with clinical parameters except for correlation between PDL-1 intensity in TILs & case age. In BCC, no detectable significant relation was found between clinicopathological characteristics& intensity as well as percentage of PDL-1 expression on TC and TILs, but there is significant negative relationship was observed between PDL-1 percentage on TC, TIL & high-risk pathological subtypes. Also, significant negative relationship was observed between PDL-1 intensity on TC& high-risk pathological subtypes.
Conclusion: PDL-1 expression on TC& TIL in SCC was significantly correlated with many tumor risk parameters such as size, pathological subtype, grade, thickness, depth of invasion, LVI and PNI. In BCC, PDL-1 expression on TC& TIL shows significantly negative correlation with age of the case & pathological subtype of the tumor.