54P Efficacy of first-line immunotherapy for non-small cell lung cancer with MET exon 14 skipping according to PD-L1 expression [Abstract]

Background METΔ14ex is the driver alteration for approximately 3% of non-small cell lung cancers (NSCLC) and associated with a higher PD-L1 expression, but unclear benefit from immunotherapy (IO). Methods Seventy-eight consecutive patients with metastatic NSCLC harboring METΔex14 who received first-line IO as monotherapy or chemoimmunotherapy (CHT+IO) in 10 German academic lung cancer centers were analyzed. Results The median age was 72 years (range 49-86), 34 patients (44%) were female, 47 (60%) were active or former smokers, and 23 (29%) presented with brain metastases. The Eastern Cooperative Group (ECOG) performance status was 0, 1, 2 and 3 in 27 (35%), 28 (36%), 18 (23%) and 4 (5%) cases, respectively. The most common histology was adenocarcinoma (n=61, 78%). IO was given to 43 (55%) patients as monotherapy, and to 35 (45%) combined with CHT. For patients with PD-L1 tumor proportion score (TPS) ≥50% (n=52, 67%), 1-49% (n=14, 18%) and <1% (n=12, 15%), disease control rates (DCR) were 56%, 57% and 100% (p=0.015), respectively. Other efficacy parameters including overall response rate (ORR), median progression-free survival (mPFS) and median overall survival (mOS) by PD-L1 tumor proportion score (TPS) and type of treatment are summarized in the table. Primary progressive disease/early death (before radiologic reassessment) under IO monotherapy, but not under CHT+IO, was significantly associated with never-smoker status (p=0.041). No significant correlations were found between smoking status and PD-L1 TPS (p=0.595). Conclusions Our exploratory analysis suggests an association between higher PD-L1 TPS and worse clinical outcomes under IO in patients with NSCLC harboring METΔ14ex. Although these results should be interpreted with caution, they contrast the favorable effect of PD-L1 expression for IO efficacy in other NSCLC and underline the need for alternative biomarkers for IO in this patient population

In Vivo Deficiency of Both C/EBPβ and C/EBPε Results in Highly Defective Myeloid Differentiation and Lack of Cytokine Response

The CCAAT/enhancer binding proteins (C/EBPs) are transcription factors involved in hematopoietic cell development and induction of several inflammatory mediators. Here, we generated C/EBPβ and C/EBPε double-knockout (bbee) mice and compared their phenotypes to those of single deficient (bbEE and BBee) and wild-type (BBEE) mice. The bbee mice were highly susceptible to fatal infections and died within 2–3 months. Morphologically, their neutrophils were blocked at the myelocytes/metamyelocytes stage, and clonogenic assays of bone marrow cells indicated a significant decrease in the number of myeloid colonies of the bbee mice. In addition, the proportion of hematopoietic progenitor cells [Lin(−)Sca1(+)c-Kit(+)] in the bone marrow of the bbee mice was significantly increased, reflecting the defective differentiation of the myeloid compartment. Furthermore, microarray expression analysis of LPS- and IFNγ-activated bone marrow-derived macrophages from bbee compared to single knockout mice revealed decreased expression of essential immune response-related genes and networks, including some direct C/EBP-targets such as Marco and Clec4e. Overall, the phenotype of the bbee mice is distinct from either the bbEE or BBee mice, demonstrating that both transcription factors are crucial for the maturation of neutrophils and macrophages, as well as the innate immune system, and can at least in part compensate for each other in the single knockout mice