Circulating tumor cells (CTC) in metastatic hepatocellular carcinoma (HCC): Comparison to control patients with nonmalignant liver diseases (NMLD) and exploratory characterization by next generation sequencing (NGS).

Abstract

207 Background: Noninvasive biomarkers are urgently needed to improve diagnosis, prognosis, and molecular characterization in HCC. Detection of CTC by EpCAM-enrichment methods is associated with poor outcomes in other tumors. Approximately 35% of HCC are EpCAM+. We hypothesized that CTC are detectable in a subset of metastatic HCC but not in NMLD and that CTC DNA might serve as a source of tumor DNA for biomarker detection and discovery. Methods: Whole blood was obtained from (1) patients with metastatic HCC and (2) NMLD controls. CTC were enumerated using CellSearch by blinded investigators. If > 10 CTC/7.5 mL, immunomagnetic enrichment for EpCAM followed by fluorescence-activated cell sorting (FACS) was also performed to collect highly purified CTC for whole genome amplification (WGA) by GenomePlex WGA4 kit. NGS using 46-gene AmpliSeq Cancer Panel (Ion Torrent) was performed on DNA from CTC, formalin-fixed paraffin embedded tumor (FFPE), and peripheral blood mononuclear cells (PBMC) if available. Results: 20 HCC and 10 NMLD were enrolled. FFPE was available in 7 HCC. In HCC cohort, median alpha-fetoprotein (AFP) was 492 ng/mL (range: 3.8-587,134) and vascular invasion (VI) was present in 13/20 (65%). CTC ≥ 3/7.5 mL were detected in 6/20 (30%, 95% CI: 0.08, 0.52) HCC and 0/9 (95% CI: 0, 0) eligible NMLD (p=0.07). One NMLD had CTC > 3/7.5 mL but was found to have HCC on surveillance ultrasound and excluded. CTC ≥ 3/7.5 mL were associated with AFP ≥ 400 (p=0.01) and VI (p=0.05) by Fisher’s exact test. NGS identified mutations listed in COSMIC in the majority including TP53 and CTNNB1. Variants appeared more frequent in CTC than FFPE in this small sample. Coverage was significantly lower in CTC than FFPE (coverage 20x mean 50% vs 93%, p < 0.02 by unpaired t-test). Conclusions: CTC are a promising biomarker in metastatic HCC and merit further study, including non-EpCAM methods. CTC were associated with AFP and VI. NGS of CTC WGA DNA is feasible and identified characteristic mutations but was limited by coverage bias. Updated NGS findings including 5 cases with paired CTC, FFPE, and/or PBMC will be presented.