• Abdallah Flaifel, Wanling Xie, David A Braun, Miriam Ficial, Ziad Bakouny, Amin H Nassar, Rebecca B Jennings, Bernard Escudier, Daniel J George, Robert J Motzer, Michael J Morris, Thomas Powles, Evelyn Wang, Ying Huang, Gordon J Freeman, Toni K Choueiri, and Sabina Signoretti.
• Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.
• Clin Cancer Res. 2019 Oct 15; 25 (20): 6080-6088.

PurposeProgrammed death-ligand 1 (PD-L1) status by IHC is prognostic in metastatic renal cell carcinoma (mRCC), and its role as a potential predictive biomarker is under investigation. Using tumor tissue from the METEOR (NCT01865747) and CABOSUN (NCT01835158) clinical trials, we explored whether PD-L1 expression and the extent of the immune cell infiltrate can serve as prognostic and/or predictive biomarkers for cabozantinib and other targeted agents.Experimental DesignIHC double staining for PD-L1 and CD45/CD163 (immune cell markers) was performed on tumor tissue from METEOR (n = 306) and CABOSUN (n = 110) clinical trials. Immune cell density and MET expression levels were also analyzed. Our primary aim was to correlate progression-free survival (PFS) by independent central review with PD-L1 status in patients treated with cabozantinib, everolimus (METEOR), or sunitinib (CABOSUN). Overall survival (OS) was also interrogated.ResultsTumor cell (TC) PD-L1 expression (≥1% cutoff) was detected in 29% and 23% of tumors from patients in the METEOR and CABOSUN trials, respectively. On univariate analysis, patients with PD-L1-positive TC had poorer PFS and OS than patients with PD-L1-negative TC on both trials, independent of therapy. On multivariable analysis and when combining the two trials, the association between TC PD-L1 expression and OS was statistically significant for all patients (P = 0.034) and for patients treated with cabozantinib only (P = 0.038). Cabozantinib was associated with improved PFS (HR < 0.70) and OS (HR < 0.85) compared with everolimus and sunitinib irrespective of PD-L1 expression.ConclusionsHigher PD-L1 expression results in worse clinical outcomes in mRCC treated with targeted therapy. Furthermore, PD-L1 expression is not predictive of response to cabozantinib therapy.©2019 American Association for Cancer Research.

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