Co-expression of PD-L1 and oncogenic receptor tyrosine kinases HER2 and cMET is low in metastatic urothelial carcinoma.

533 Background: Activation of HER2 and cMET signaling has been implicated in the pathogenesis of urothelial carcinoma subsets, and the use of anti-PD-(L)1 agents is well established in this disease. Novel therapeutic combinations targeting both immune checkpoints and the cMET or HER2 pathways are currently under investigation in metastatic urothelial carcinoma (mUC). Co-expression of these molecular targets has not been characterized in mUC. We hypothesized that the rate of PD-L1 co-expression with cMET and HER2 may be low. Therefore, we sought to define tumor protein co-expression of PD-L1, HER2 and cMET in a cohort of mUC patients. Methods: Patients with mUC were identified from an institutional database. FFPE tumor specimens from metastatic sites and available paired primary tumors underwent immunohistochemical staining for PD-L1 (SP-142), cMET, and HER2 expression. High expression was defined using the following thresholds: PD-L1: >=5% of infiltrated immune cells; cMET: >=50% of tumor cells; HER2: score=3+ (complete membrane staining that is intense and >10% of tumor cells). Simple and Weighted Cohen’s kappa Statistics (κ) were utilized to assess the agreement in expression and co-expression between paired primary and metastatic samples. Cohen’s interpretation of the κ results is provided. Results: Specimens from 143 mUC patients were analyzed, including 79 with available paired primary tumors. In primary tumors (N=79), high expression of PD-L1, cMET, and HER2 was observed in 15.2%, 34.2%, and 12.7%, respectively. In metastatic samples (N=143), high expression of PD-L1, cMET and HER2 was detected in 9.8%, 41.3%, and 9.8%, respectively. Expression agreement rates between primary and metastatic specimens (n=79) were PD-L1: 79.7% (κ=0.09, slight agreement), cMET: 69.6% (κ=0.35, fair agreement), HER2: 84.8% (κ=0.17, slight agreement) and were driven by high prevalence of low expression. High PD-L1/cMET co-expression was observed in only 5.1% (n = 4) of primary and 4.9% (n =7) of metastatic specimens. High co-expression of PD-L1/HER2 occurred in only 3.8% (n=3) of primary samples and in no metastatic samples. The overall co-expression agreement rate between paired primary and metastatic samples was 55.7% (κ = 0.22, fair agreement) for PD-L1/cMET and 67.1% (κ = 0.06, slight agreement) for PD-L1/HER2. Importantly, however, agreements rates for high co-expression between primary and metastatic samples were very low (2.5% for PD-L1/cMET and 0% for PD-L1/HER2). Conclusions: Tumor co-expression of high cMET or HER2 and PD-L1 is low in this cohort of metastatic urothelial carcinoma patients. Furthermore, agreement of high co-expression between primary and metastatic sites is rare. These results suggest that investigational strategies combining immune checkpoint inhibition with either cMET or HER2 targeted agents in mUC may have limited synergistic activity.