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  • Title: Higher concordance of PD-L1 expression between biopsies and effusions in epithelioid than in nonepithelioid pleural mesothelioma.
    Author: Mansour MSI, Seidal T, Mager U, Dobra K, Brunnström H, Dejmek A.
    Journal: Cancer Cytopathol; 2021 Jun; 129(6):468-478. PubMed ID: 33493383.
    Abstract:
    BACKGROUND: Malignant mesothelioma (MM) is a therapy-resistant tumor, often causing an effusion. Drugs targeting the programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway have shown promising results, but assessment of PD-L1 expression to select patients for therapy has mainly been performed on histologic tissue samples. In a previous study, we showed that MM effusions are suitable for PD-L1 assessment with results comparable to those reported in histologic studies, but no studies have compared PD-L1 expression in histologic and cytologic samples. METHODS: PD-L1 expression was determined immunohistochemically (clone 28-8) in 61 paired samples of effusions and biopsies from patients with pleural MM, obtained at the time of diagnosis. Only cases with >100 tumor cells were included. Membranous staining in tumor cells was considered positive at ≥1%, >5%, >10%, and >50% cutoff levels. RESULTS: Of 61 histologic samples, PD-L1 expression was found in 28 and 7 samples at ≥1% and >50% cutoffs, respectively; the corresponding figures for cytology were 21 and 5, respectively. The overall percentage agreement between histology and cytology was 69% and 84%, with a kappa (κ) of 0.36 and 0.08 at ≥1% and >50% cutoffs, respectively. The concordance between cytology and histology tended to be higher for epithelioid MM versus nonepithelioid MM at a ≥1% cutoff. PD-L1 positivity in biopsies, but not in effusions, correlated with the histologic subtype at a ≥1% cutoff. CONCLUSIONS: A moderate concordance of PD-L1 expression between biopsies and effusions from pleural MM, especially for the epithelioid subtype, indicates biological differences between the 2 types of specimens. Cytology and histology may be complementary.
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