Dynamic and immunocytochemistry analysis of circulation tumor cells (CTCs) in blood samples from patients with advanced ccRCC starting first-line treatment in a Brazilian Cancer Center.

Abstract

704 Background: Treatment of advanced clear cell renal carcinoma (ccRCC) improved dramatically in the last 20 years, but biomarkers development lagged behind. Circulating tumor cell (CTC) is used as a prognostic and predictive tool in many solid tumors but is poorly studied in ccRCC. Objective: Our aim was to evaluate CTC counts in serial blood samples from patients with advanced ccRCC that started first-line treatment and analyze the protein expression of PBRM1, BAP1, PD-L1 and CD133 in these cells. Methods: Blood samples (10mL) were collected in EDTA tubes at three different timepoints, 30 days apart, after treatment start. We used a filtration technique (ISET system, Rarecells/France) to isolate and collect CTCs. Protein expression was evaluated by immunocytochemistry. Results: Twelve patients were included. All had detectable CTCs at baseline (1st blood draw), with a median of 1.5 CTCs/mL. Patients with CTCs above the median had ≥2 metastatic sites (p=0.015) and worse progression free survival (PFS) (19.7 vs 31.1 months, p=0.35), although the difference was not statistically different. Favorable CTCs kinetics at the time of first follow-up (2nd blood draw) indicated better PFS (24.76 months) versus unfavorable (6.65 months; p=0.014). PBRM-1, BAP-1 and PD-L1 expression in CTCs was associated with better overall survival (OS), although without statistical significance. CD133 expression in CTCs at baseline was associated with worse OS (p=0.08). Conclusions: CTCs isolation was feasible in advanced ccRCC patients starting first-line treatment and were frequently detected by ISET method. CTC counts at baseline and at 30 days after treatment initiation had prognostic implication, as well as its dynamic evaluation after 30 days of treatment with a favorable kinetics associated with better outcome.