Detection of tumor-derived cell-free DNA from colorectal cancer peritoneal metastases in plasma and peritoneal fluid

Abstract

Tumor-derived cell-free DNA (cfDNA) is an emerging biomarker for guiding the personalized treatment of patients with metastatic colorectal cancer (CRC). While patients with CRC liver metastases (CRC-LM) have relatively high levels of plasma cfDNA, little is known about patients with CRC peritoneal metastases (CRC-PM). This study evaluated the presence of tumor-derived cfDNA in plasma and peritoneal fluid (i.e. ascites or peritoneal washing) in 20 patients with isolated CRC-PM and in the plasma of 100 patients with isolated CRC-LM. Among tumor tissue KRAS/BRAF mutation carriers, tumor-derived cfDNA was detected by droplet digital polymerase chain reaction (ddPCR) in plasma of 93% of CRC-LM and 20% of CRC-PM patients and in peritoneal fluid in all CRC-PM patients. Mutant allele fraction (MAF) and mutant copies per ml (MTc/ml) were lower in CRC-PM plasma than in CRC-LM plasma (median MAF = 0.28 versus 18.9%, p < 0.0001; median MTc/ml = 21 versus 1,758, p < 0.0001). Within patients with CRC-PM, higher cfDNA levels were observed in peritoneal fluid than in plasma (median MAF = 16.4 versus 0.28%, p = 0.0019; median MTc/ml = 305 versus 21, p = 0.0034). These data imply that tumor-derived cfDNA in plasma is a poor biomarker to monitor CRC-PM. Instead, cfDNA detection in peritoneal fluid may offer an alternative to guide CRC-PM treatment decisions.

Keywords: ascitic fluid; biomarkers; circulating tumor DNA; colorectal neoplasms; liquid biopsy; peritoneum; plasma.

Figure 1

Among patients with a tumor tissue KRAS/BRAF mutation, the percentage of patients in whom a KRAS/BRAF mutation was also detected: (left) in plasma of patients with isolated CRC‐LM; (middle) in plasma of patients with isolated CRC‐PM; and (right) in peritoneal fluid of patients with isolated CRC‐PM.

Figure 2

(A) MTc/ml plasma or peritoneal fluid and (B) MAF measured in plasma of patients with isolated CRC‐LM (N = 57), in plasma of patients with isolated CRC‐PM (N = 10), and in peritoneal fluid of patients with isolated CRC‐PM (N = 8). Red symbols: patients with a resected primary tumor at the time of blood and peritoneal fluid collection. Green symbols: patients with an unresected primary tumor at the time of blood and peritoneal fluid collection. ns, Not significant; ****p < 0.0001.