Circulating Tumor Cell Subtypes and T-cell Populations as Prognostic Biomarkers to Combination Immunotherapy in Metastatic Genitourinary Cancer Patients.

Purpose: Circulating tumor cells (CTCs) are under investigation as a minimally invasive liquid biopsy that may improve risk stratification and treatment selection. CTCs uniquely allow for digital pathology of individual malignant cell morphology and marker expression. We compared CTC features and T-cell counts with survival endpoints in a cohort of metastatic genitourinary (mGU) cancer patients treated with combination immunotherapy. Experimental Design: Markers evaluated included pan-CK/CD45/PD-L1/DAPI for CTCs and CD4/CD8/Ki-67/DAPI for T cells. ANOVA was used to compare CTC burden and T-cell populations across time points. Differences in survival and disease progression were evaluated using the maximum log-rank test. Results: From 12/2016-01/2019, 183 samples from 81 patients were tested. CTCs were found in 75% of patients at baseline. CTC burden was associated with shorter OS at baseline (p=0.022) but not on therapy. Five morphologic subtypes were detected, and the presence of 2 specific subtypes with unique cellular features at baseline and on therapy were associated with worse OS (0.9-2.3 mos vs. 28.2 mos,p<0.0001-0.013). Increasing CTC heterogeneity on therapy had a trend towards worse OS (p=0.045). PDL1+ CTCs on therapy were associated with worse OS (p<0.01,cycle 2). Low baseline and on-therapy CD4/CD8 counts were also associated with poor OS and response category. Conclusions: Shorter survival may be associated with high CTC counts at baseline, presence of specific CTC morphologic subtypes, PD-L1+ CTCs, and low %CD4/8 T cells in mGU cancer patients. A future study is warranted to validate the prognostic utility of CTC heterogeneity and detection of specific CTC morphologies.