Rolf A. Stahel

8516 Background: Conflicting data exists on the potential prognostic impact of PD-L1 expression in NSCLC. The Lungscape project, a fully annotated large biobank of resected stage I-III NSCLC, allows detailed analysis of this issue. Methods: Prevalence of PD-L1 positivity and its association with clinicopathological characteristics and patient outcome - Relapse-free Survival (RFS), Time-to-Relapse (TTR) and Overall Survival (OS) - was explored in the ETOP Lungscape cohort. PD-L1 expression was assessed on tissue microarrays (TMAs) using the DAKO 28-8 immunohistochemistry assay. Positivity cut-off points of ≥1%, 5% and 50% for neoplastic cell membrane staining were considered. Results: PD-L1 data were available for 2182 patients, from 15 ETOP centers, with median follow-up 4.8 years; 1191 patients still alive; median age 66 years; 64% male, 32/54/11% for current/former/never smokers; 49/29/22% for stages I/II/III; 51/42/4/3% adenocarcinomas (AC)/squamous cell (SCC) /large cell and sarcomatoid (LCS)/other. Median RFS/TTR/OS were 53/99/69 months (AC: 52/84/72, SCC: 54/not reached/64; and LSC 52/103/74). PD-L1 prevalence with 1% cut-off was, overall: 43%, 95% confidence interval (95%CI): 41-46; (AC: 42%, 95%CI: 39-46; SCC: 44%, 95%CI: 40-47; and LCS: 53%, 95%CI: 42-65), while for 5% threshold, prevalence was 34%, 95%CI: 32-36. PD-L1 1% positivity was a significant predictor only for AC: HR_{RFS: + vs -} = 0.82; 95%CI: 0.69-0.97, HR_{TTR: + vs -} = 0.83; 95%CI: 0.68-1.01, HR_{OS: + vs -}= 0.83; 95%CI: 0.69-1.01 (adjusted p = 0.024, 0.064, 0.063 respectively). This effect is found also for the 5% cut-off, and preserved in the overall model including all histologies. Using the 50% cut-off, PD-L1 positivity was detected in 17% of patients; 95%CI: 15-18, but was no longer a significant predictor of outcome, overall and by histology type. Conclusions: PD-L1 positivity (1% and 5% cut-offs) was present in more than one third of resected NSCLC and was associated with a better prognosis for AC patients.

Cellular resistance to etoposide has been correlated both with reduced levels and an aberrant cytoplasmic accumulation of the drug`s target, topoisomerase IIα (topo IIα). It is not known, however, whether a cytoplasmic pool of topo IIα is sufficient to confer drug resistance on cultured mammalian cells. In our study, we have transfected mouse fibroblasts and human 293 cells with truncated forms of human topo IIα fused to GFP and have examined the transformants for the subcellular localization of topo IIα and their resistance to etoposide. Transient transfection resulted in high-level expression of all GFP-topo IIα fusions tested, whereas in stably transfected cells the levels varied significantly. Transfectants expressing a central or a carboxy-terminal topo IIα domain (aa 428-1504, 639-1028 or 1028-1504) accumulated high levels of the fusion proteins, while only very low amounts of GFP-topo IIα proteins were observed in cell lines expressing constructs that retain the amino-terminus of the enzyme (aa 1-1214, aa 1-939, aa 1-611). Our results suggest that the topo IIα amino-terminus affects the stability of truncated forms of the enzyme in mammalian cells, perhaps due to targeted degradation. Assays that screen for cell vitality and DNA synthesis reveal no significant changes in etoposide sensitivity in transfected cells expressing high levels of cytoplasmic or nuclear localized topo II fusion proteins. Retroviral expression of a cytoplasmically anchored domain of human topo IIα also failed to confer drug resistance. These results suggest that a cytoplasmic pool of topo IIα is not sufficient to render cultured mammalian cells drug resistant. Int. J. Cancer 88:99–107, 2000.