Author of

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  P37 - Pathology - Biomarker Testing (ID 107)

  • Event: WCLC 2020
  • Type: Posters
  • Track: Pathology, Molecular Pathology and Diagnostic Biomarkers
  • Presentations: 1
  • Moderators:
  • Coordinates: 1/28/2021, 00:00 - 00:00, ePoster Hall

  • 34792

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    P37.10 - PD-L1 Expression in Lymphovascular Tumor Emboli in Lung Adenocarcinoma (ID 3113)

    00:00 - 00:00  |  Presenting Author(s): Yi-Chen Yeh
    • Abstract
    • Slides

    Introduction
    

    PD-L1 expression by immunohistochemistry is the most widely used predictive biomarker of response to immune checkpoint inhibitors. Compared with PD-L1 expression in tumor tissue, the characteristics of PD-L1 expression in circulating tumor cells (CTCs) are less well understood. A major obstacle to study PD-L1 expression in CTCs is the lack of standardized method for PD-L1 expression detection in CTCs. All of the USFDA-approved standard PD-L1 assays are intended to use in tissue sections only, and not applicable to CTCs isolated from peripheral blood. In tumor tissue sections, clusters of CTCs inside lymphovascular spaces, which are known as lymphovascular tumor emboli, can be observed in around 30% of surgically resected lung cancer. Because these lymphovascular tumor emboli are present in tissue sections, it is possible to use standard PD-L1 assay for tissue to evaluate their PD-L1 expression. To further characterize PD-L1 expression in the tumor cells within lymphovascular tumor emboli, in this study we investigated PD-L1 expression in lung cancer tumor tissue, lymphovascuar tumor emboli, and lymph node metastasis using the standard Dako PD-L1 IHC 22C3 pharmDx assay.

    Methods
    

    We included 26 cases of surgically resected lung adenocarcinoma with extensive lymphovascular emboli and lymph node metastasis in this study. Whole tissue sections were stained with Dako PD-L1 IHC 22C3 pharmDx assay. PD-L1 expression was scored in primary tumor, lymphovascular emboli, and lymph node metastasis respectively by a pathologist using Tumor Proportion Score (TPS). Positive PD-L1 expression is defined as TPS≧1%. McNemar's test was used to compare the frequencies of PD-L1 expression between different groups.

    Results
    

    The frequencies of positive PD-L1 expression in primary tumor, lymphovascular emboli and lymph node metastasis are 31%, 8%, and 23%, respectively. There is significant lower PD-L1 expression in lymphovascular emboli compared with primary tumor (P=0.031). No difference in PD-L1 expression is found between primary tumor and lymph node metastasis (P=0.625). PD-L1 expression is discordant between primary tumor and lymphovascular emboli in 23% of the cases. The detailed results of each cases and distribution of TPS are summarized in Figure 1.

    

    Conclusion
    

    There is significant difference of PD-L1 expression between primary tumor and lymphovascular emboli. Tumor cells in lymphovascular emboli have lower PD-L1 expression compared with primary tumor. Whether such difference is related to the intrinsic tumor cell heterogeneity or extrinsic factors such as microenvironment warrant further investigations.

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