Correlation of PD-L1 Expression with Histological Patterns and Treatment Response in Non-Small Cell Lung Cancer

Programmed Death Ligand-1 (PD-L1) inhibitors are currently approved for treatment of advanced stage NonSmall Cell Lung Cancer (NSCLC) patients. We investigated the correlation between PD-L1 expression level in tumor cells by ImmunoHistochemical Method (IHC) to tumor histological growth patterns. Slides or scanned digital images of NSCLC cases tested for PD-L1 between December, 2016 to April, 2018 were blindly re-reviewed to confirm the PD-L1 expression and growth patterns. PD-L1 expression levels were graded as follows: < 1%, negative, 1-50%, low expression, > 50%, high expression. Total 102 cases were identified including 81 cases of adenocarcinoma and 21 cases of Squamous Cell Carcinoma (SCC). Variable expression was seen in SCC; 8/21 cases (38%) showed negative expression of PD-L1, 7/21 cases (33%) showed low expression, and 6/21 cases (29%) showed high expression. 4/6 total “high-expression” SCC cases (67%) demonstrated poorly differentiated/non-keratinizing pattern, while 2/6 (33%) were wellto Moderately-Differentiated/ keratinizing SCC. In wellto Moderately-Differentiated (WD to MD) adenocarcinoma, 15/30 cases (50%) showed negative expression of PD-L1, 13/30 cases (43%) showed low expression, whereas only 2/30 cases (7%) had high expression. On the other hand, moderateto poorlydifferentiated (MD to PD) adenocarcinomas, 13/51 cases (26%) showed negative expression of PD-L1, 15/51 cases (29%) showed low expression and 23/51 cases (45%) had high expression. 21/25 total "high-expression" cases (84%) demonstrated poorly-differentiated growth patterns, out of which, 7 cases (33%) had a pure solid growth pattern. A 1-year follow up showed 3 patients with partial or complete response, whose tumors had “high-expression” PD-L1.