Li, Jian

To evaluate the clinical utility of cell‐free DNA (cfDNA), we performed whole‐genome sequencing to systematically examine plasma cfDNA copy number variations (CNVs) in a cohort of patients with colorectal cancer (CRC, n = 80), polyps (n = 20), and healthy controls (n = 35). We initially compared cfDNA yield in 20 paired serum–plasma samples and observed significantly higher cfDNA concentration in serum (median = 81.20 ng, range 7.18–500 ng·mL−1) than in plasma (median = 5.09 ng, range 3.76–62.8 ng·mL−1) (P < 0.0001). However, tumor‐derived cfDNA content was significantly lower in serum than in matched plasma samples tested. With ~10 million reads per sample, the sequencing‐based copy number analysis showed common CNVs in multiple chromosomal regions, including amplifications on 1q, 8q, and 5q and deletions on 1p, 4q, 8p, 17p, 18q, and 22q. Copy number changes were also evident in genes critical to the cell cycle, DNA repair, and WNT signaling pathways. To evaluate whether cumulative copy number changes were associated with tumor stages, we calculated plasma genomic abnormality in colon cancer (PGA‐C) score by summing the most significant CNVs. The PGA‐C score showed predictive performance with an area under the curve from 0.54 to 0.84 for CRC stages I‐IV. Locus‐specific copy number analysis identified nine genomic regions where CNVs were significantly associated with survival in stage III‐IV CRC patients. A multivariate model using six of nine genomic regions demonstrated a significant association of high‐risk score with shorter survival (HR = 5.33, 95% CI = 6.76–94.44, P < 0.0001). Our study demonstrates the importance of using plasma (rather than serum) to test tumor‐related genomic variations. Plasma cfDNA‐based tests can capture tumor‐specific genetic changes and may provide a measurable classifier for assessing clinical outcomes in advanced CRC patients.

152 Background: Plasma cfDNA ARcopy number variations (CNV) have been suggested to have prognostic significance in mCRPC stage. We compared plasma AR amplification ( ARamp) with CTC counts (the only FDA approved prognostic marker in mCRPC stage) in a prospective trial of patients (pts) progressing on androgen deprivation therapy. Methods: Plasma and CTC counts were obtained concurrently as part of a prospective clinical trial in mCRPC stage pts initiating abiraterone acetate (NCT# 01953640). Plasma cfDNA was purified using DNA Blood Mini Kit (Qiagen, Valencia, CA) and AR CNVs were detected using QuantStudio3D digital PCR system (Life Technologies, Carlsbad, CA, USA). CTC enumeration was performed using the FDA cleared CellSearch platform. The distributions of overall survival (OS) time based on ARamp status and CTC counts ( < 5 vs ≥ 5 cells) were estimated using the Kaplan-Meier method. Log-rank tests were used to test association of ARamp status and CTC counts with overall survival (OS). Univariate and multivariate logistic regression models and ROC evaluated association of OS at 24 months by ARamp status and CTCs ≥ 5. Results: Between 05/2013 and 09/2015, 92 pts were enrolled of which complete CTC, plasma and outcome data was available for 70 pts. Median age of the cohort (range) was 72 yrs (39-91); Median PSA–16.2 ng/ml (range: 0.9-2026.0); Median CTC count was 2.0 (range: 0-372); 58/70 pts had bone metastases; 38/70 had high volume and 32/70 had low volume metastatic disease at the time of sample collection. The median (range) follow up time at the time of this analysis was: 26.5 (7.9-37.0) months at which time 28/70 patients had died. ARamp was present in 19/70 pts while 51/70 did not have amplification. 24/70 had CTCs ≥ 5. A significant association of increased ARamp status with OS (p < 0.0001, log-rank test; AUC: 0.66) as well as with CTC counts ≥ 5 (p = 0.001, log-rank test; AUC: 0.67) was observed. Combining CTC status and plasma ARamp status the AUC was 0.75. Conclusions: Plasma cfDNA ARamp status and CTC counts have comparable and clinically meaningful prognostic marker value in mCRPC stage patients.