Maria Korah, MD
General Surgery Resident
Stanford University
Stanford, California, United States
Beatrice J. Sun, MD, MS (she/her/hers)
Resident
Stanford University School of Medicine
Stanford, California, United States
James P. Agolia, MD
General Surgery Resident
Stanford University
Stanford, California, United States
George Poultsides, MD
Professor
Stanford University
Stanford, California, United States
Byrne Lee, MD (he/him/his)
Clinical Professor, Surgery
Stanford University
Stanford, California, United States
Daniel Delitto, MD PhD
Assistant Professor of Surgery
Stanford University
Stanford, California, United States
Lumeng J. Yu, MD (she/her/hers)
Surgical Oncology Fellow
Stanford University
Stanford, California, United States
Pressurized intraperitoneal aerosolized chemotherapy (PIPAC) is an emerging locoregional treatment for peritoneal metastases (PM), allowing for more even distribution of drug delivery and improved tumor penetration. While clinical and pathological outcomes, including peritoneal cancer index (PCI) and peritoneal regression grading score (PRGS), have been reported for gastrointestinal malignancies with PM undergoing PIPAC, the cellular and molecular changes in the peritoneal immune microenvironment remain incompletely understood. We sought to characterize transcriptomic alterations in ascites before and after PIPAC using single cell RNA sequencing (scRNAseq).
Methods: Patients enrolled in an ongoing prospective PIPAC registry trial with peritoneal metastases from appendiceal, gastric, or colorectal primaries were included. Ascites and four quadrant biopsies were collected prior to the first PIPAC and second PIPAC administration. All patients had received ≥12 cycles of systemic chemotherapy before trial enrollment and received another cycle of systemic chemotherapy between the first and second round of PIPAC. Single-cell suspensions were processed using 10X Genomics protocols and analyzed with the scanpy pipeline. PCI was recorded at each PIPAC, and PRGS was reported for the four quadrant biopsies.
Results:
A total of six ascites samples from three patients were analyzed, yielding 18,876 high quality cells. Two patients had metastatic mucinous appendiceal adenocarcinoma. The third patient had metastatic gastric adenocarcinoma. All ascites samples were comprised of heterogenous microenvironments comprised of mesothelial cells, macrophages, dendritic cells, T cells, NK cells, B cells, and plasma cells. The microenvironment evolved following PIPAC in every patient, with a decrease in myeloid cells (75.8% to 60.8%) and an increase in T/NK cells (19.8% to 31.5%). PCI scores remained stable for two patients and improved from 30 to 22 after one round of PIPAC for one patient with appendiceal adenocarcinoma. These correlated with a PRGS of 3 for the patient with gastric adenocarcinoma, and 2 for the two patients with appendiceal adenocarcinoma.
Conclusions: To our knowledge, we present the first scRNA-seq atlas of the peritoneal microenvironment of patients undergoing PIPAC. Our findings suggest that PIPAC induces an evolution of the peritoneal immune microenvironment. Further investigation into the mechanism of PIPAC is needed to optimize treatment strategies for peritoneal metastasis.