Comparing patient reported abdominal pain between patients treated with oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy (PIPAC-OX) and primary colorectal cancer surgery

Oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy (PIPAC-OX) is an emerging palliative treatment for patients with unresectable colorectal peritoneal metastases. Previously, our study group reported that patients experienced abdominal pain for several weeks after PIPAC-OX. However, it is unknown how this compares to abdominal pain after regular colorectal cancer surgery. To provide some perspective, this study compared the presence of abdominal pain after PIPAC-OX to the presence of abdominal pain after primary tumor surgery. Patient reported abdominal pain scores (EORTC QLQ-CR-29), from two prospective, Dutch cohorts were used in this study. Scores ranged from 0 to 100, a higher score represents more abdominal pain. Abdominal pain at baseline and at four weeks after treatment were compared between the two groups. Twenty patients who underwent PIPAC-OX and 322 patients who underwent primary tumor surgery were included in the analysis. At baseline, there were no differences in abdominal pain between both groups (mean 20 vs. 18, respectively; p = 0.688). Four weeks after treatment, abdominal pain was significantly worse in the PIPAC group (39 vs 15, respectively; p < 0.001; Cohen's d = 0.99). The differential effect over time for abdominal pain differed significantly between both groups (mean difference: 19 vs - 3, respectively; p = 0.004; Cohen's d = 0.88). PIPAC-OX resulted in significantly worse postoperative abdominal pain than primary tumor surgery. These results can be used for patient counseling and stress the need for adequate analgesia during and after PIPAC-OX. Further research is required to prevent or reduce abdominal pain after PIPAC-OX.Trial registration CRC-PIPAC: Clinicaltrails.gov NCT03246321 (01-10-2017).

Abstract 708: Limited release of circulating tumor DNA into the systemic circulation by peritoneal metastases from colorectal cancer

Introduction: Circulating tumor DNA (ctDNA) from plasma is a promising biomarker. Patients with metastatic colorectal cancer (CRC) often have high ctDNA levels compared to other cancer types. However, it is unclear whether this is also the case for patients with peritoneal metastases from CRC.

Aim: To compare the propensity of ctDNA shedding by isolated liver metastases and isolated peritoneal metastases from CRC.

Methods: Plasma was collected from 100 CRC patients (64% male, mean age of 60 [SD=10] years) with isolated unresectable liver metastasis (CRC-LM). Plasma and ascites were obtained from 20 CRC patients (60% male, mean age of 63 [SD=9.8] years) with isolated unresectable peritoneal metastases (CRC-PM). All liquid biopsies were obtained prior to treatment and cell-free DNA was isolated using the QIAsymphony (Qiagen, Germany) and assessed by droplet digital PCR (ddPCR; Bio-Rad, Hercules, USA). Patients with a KRAS or BRAF tumor tissue mutation were suited for plasma ctDNA ddPCR analysis, and were detected in 57 CRC-LM (57%) and 11 CRC-PM (55%) patients. The ability to shed ctDNA into the circulation was evaluated by comparing KRAS/BRAF mutation status in plasma and ascites with the mutation status based on tumor tissue. Regarding liquid biopsies, mutant allele fraction (MAF) and mutant copies per ml input (MTc/ml) were reported.

Results: Tissue mutations could be confirmed in plasma in 93% of CRC-LM and only 20% of CRC-PM patients, whereas mutations were detected in ascites in 100% of CRC-PM patients. The MAF and MTc/ml were both significantly lower in CRC-PM plasma ctDNA (median MAF=0.28% and MTc/ml=21) compared to CRC-LM plasma ctDNA (median MAF=18.9% and MTc/ml= 1758; P&lt;0.0001). In addition, the MAF and MTc/ml were significantly higher in CRC-PM ascites ctDNA (median MAF=16.4%, MTc/ml=305) compared to plasma ctDNA (median MAF=0.28%, MTc/ml=21; P&lt;0.0001).

Conclusion: To our knowledge, this is the first study showing a comprehensive comparison of tissue, blood and ascites derived genomic information in patients with CRC and extensive isolated peritoneal metastases. This study concludes that isolated peritoneal metastases from CRC is a malignancy with distinct clinical and biological characteristics, which should be taken into account when considering the clinical utility of ctDNA in different metastatic setting of CRC. To detect genomic alterations, the blood circulation is the preferred source of ctDNA in case of CRC liver metastases, whereas ascites offers an alternative to plasma in patients with peritoneal metastases, which might be suitable as diagnostic, prognostic, predictive or disease monitoring biomarker.

Citation Format: Iris van 't Erve, Koen P. Rovers, Alexander Constantinides, Karen Bolhuis, Emma C. Wassenaar, Robin J. Lurvink, Clément J. Huysentruyt, Petur Snaebjornsson, Daan van den Broek, Tineke E. Buffart, Niels F. Kok, Gerrit A. Meijer, Cornelis J. Punt, Onno Kranenburg, Ignace H. de Hingh, Remond J. Fijneman. Limited release of circulating tumor DNA into the systemic circulation by peritoneal metastases from colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 708.