PD-L1 expression and clinical outcomes to cabozantinib, everolimus and sunitinib in patients with metastatic renal cell carcinoma: analysis of the randomized clinical trials METEOR and CABOSUN

Purpose: PD-L1 status by immunohistochemistry (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 Design: IHC 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. Results: 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 on cabozantinib only (p=0.038). Cabozantinib was associated with improved PFS (HR