117P - Evaluation of tumor- and stromal immune marker heterogeneity in non-small cell lung cancer

Abstract

Immunotherapy is the current standard in second-line treatment for non-small cell lung cancer (NSCLC) patients. However, accurate identification of patients who benefit based on immune marker (IM) expression remains a challenge. Here, we aimed to estimate the potential impact of heterogeneity on the assessment of IM expression in both lung adenocarcinoma (ADC) and squamous-cell carcinoma (SCC). A total of 144 surgically treated NSCLC patients were included, 94 ADCs and 50 SCCs. Two tumor cores per patient were incorporated into tissue microarrays (TMA). CD3 and CD8 were assessed by immunohistochemistry (IHC) and PD-L1 by IHC and FISH. Expression of IM was analyzed both in tumor cells (TC) and tumor stroma (TS). A PD-L1 positivity threshold of ≥1% was established for IHC and PDL1 gene amplification was defined as a PDL1/CEP9 ratio of ≥2. In each core, CD3 and CD8 positive cells were recorded quantitatively and the CD8/CD3 ratio was calculated. Heterogeneity of IM between corresponding tumor cores was analyzed using kappa agreement index. Finally, IM expression was correlated with clinical, pathological and molecular variables. Patients' median age was 65, 80% were male and 46% were current smokers. PD-L1 was expressed in TC and TS in 22% and 62% of cases, respectively. Amplification of PDL1 was found in 12 of cases, of which 8 (67%) were IHC PD-L1 positive in TC. Heterogeneity of TC PD-L1 positivity was 8% in ADC and 6% in SCC. Regarding TS PD-L1 expression, discordance between corresponding cores was found in 19% and 34% of ADC and SCC cases, respectively. PDL1 amplification was discordant between cores in 5 of 12 (42%) cases. Per core, median CD3 and CD8 positive cells were 436 and 159, respectively. Median CD8/CD3 ratio was 0.23 in ADC and 0.53 in SCC. Taking these values as cut-off points, CD8/CD3 ratio was discordant in 22% and 10% of ADC and SCC cases, respectively. Finally, TC PD-L1 expression was correlated with CD8 infiltrate. (p < 0.05 for ADC and SCC). PD-L1 IHC expression appears to be more heterogeneous when assessed in the TS compared to the TC compartment, especially in SCC histology. Intra-tumor heterogeneity has to be taken into account when selecting patients for immunotherapy based on PD-L1 positivity or lymphocyte presence.