Intra-patient heterogeneity in urothelial cancer (UC) circulating tumor cells (CTC) and PDL1 expression to identify biomarkers of response and new therapeutic targets: A pilot study.

Abstract

4537 Background: Recent use of immune checkpoint inhibitors (CI) has improved overall survival (OS) in a subset of patients (pts) with metastatic UC. Intra-patient tumoral heterogeneity and epithelial-to-mesenchymal transition has been hypothesized as a driver of treatment resistance to both chemotherapy and CI in UC. There is a critical need to evaluate heterogeneity in UC for biomarkers of treatment response and new therapeutic targets. Trop2 is hypothesized to play a role in UC progression and is the target of a new antibody-drug conjugate, IMMU-132 that is being tested in UC trials. We report the phenotypic comparison of PDL1 expression among CTC subpopulations in UC pts. Methods: Peripheral blood samples were collected from pts with UC treated at Cleveland Clinic and U. of Wisconsin. Immunomagnetic capture and CTC enumeration using both EpCAM and Trop2 from matched blood samples was performed in the VERSA platform. Protein expression for PDL1 in these CTC populations was quantified. Longitudinal analysis of UC pts treated with chemotherapy or CI is ongoing. Results: CTC were captured using EpCAM and Trop2 in all 10 pts in our initial cohort. The frequency of Trop2 CTC was higher than EpCAM CTC with a mean of 248 Trop2 CTC (range 2-1885) compared to 76 EpCAM CTC (range 1-632). PDL1 expression was more frequent in Trop2 CTC than EpCAM CTC. In two pts progressing on Atezolizumab, Trop2 CTC had a higher frequency of PDL1 expression compared to EpCAM CTC (85% vs 2% in pt 1 and 2% vs 0% in pt 2). In pts followed longitudinally, Trop2 CTC dropped from 1885 to 1 in a pt with response to Atezolizumab and PDL1+ CTC declined from 4 to 0. After 1 cycle of Carbo/Gem in another pt, EpCAM CTC declined from 46 to 3 while Trop2 CTC from 116 to 47. Conclusions: This is the first report of CTC heterogeneity in pts with UC identifying high frequency of Trop2 CTCs with variable expression of PDL1 across different pts. Early results from longitudinal analysis suggest CTC as potential predictive / pharmacodynamic biomarkers of treatment response. Prospective data validation in larger cohort is ongoing, while IMMU-132 clinical trials in UC may provide context for future validation.