PM18 - Peritoneal Cell-Free Tumor DNA as a Biomarker of Disease Burden in Peritoneal Carcinomatosis

Background: Disease burden in patients with peritoneal carcinomatosis (PC) is difficult to estimate. We evaluated whether peritoneal cell-free tumor DNA can be used as a measure of disease burden.

Methods: Malignant ascites or peritoneal lavage fluids were collected from patients with PC under approved IRB protocol. Cell-free DNA was extracted from peritoneal fluids using QIAGEN DNA extraction kit. Droplet digital PCR (ddPCR) was performed using BioRad ddPCR KRAS G12/G13 screening kit according to manufacturer’s instructions.

Results: Cell-free mutant KRAS DNA was detected in 11/14 (79%) malignant peritoneal fluids with a mutant allele frequency (MAF) of 0.1% to 26.1%. While peritoneal cell-free KRAS mutant DNA was detected in all the patients with KRAS mutant tumors (N=7), 3/4 (75%) patients with KRAS wild-type tumors also had peritoneal cell-free KRAS mutant DNA, suggesting improved sensitivity to detect KRAS mutants. We also found that 75% (3/4) of patients with cytoreducible disease had a MAF of < 1% (median: 0.3%, range: 0.1-4.7%), while 71% (5/7) of patients with unresectable disease had a MAF of > 1% (median: 4.4%, range: 0.1-26%).

Conclusions: This pilot study suggests that cell-free tumor DNA detected by ddPCR may enable prediction of disease burden and resectability in patients with PC.