Molecular Testing May Offer a New Way to Improve Staging of Gastric Cancer
Neilson T, Seldomridge A, Smith PM, Maher M, Ikoma N, Badgwell BD, White MG. Evaluating gastric peritoneal washing supernatant NGS integration to inform staging of peritoneal metastases. Surgical Oncology Insight. 2026;3(3):100286. doi:10.1016/j.soi.2026.100286.
Accurately determining whether gastric cancer has spread to the lining of the abdomen—the peritoneum—is an important part of treatment planning. Yet small amounts of peritoneal disease can be difficult to detect with imaging alone, and even traditional peritoneal washing cytology may miss cancer cells when only a very small amount of disease is present.
A new study published in Surgical Oncology Insight explores whether next-generation sequencing (NGS) of fluid collected during peritoneal washing could provide additional information to help identify peritoneal metastases in patients with gastric cancer. The study, conducted by researchers at The University of Texas MD Anderson Cancer Center, examined the potential of analyzing the supernatant, or cell-free liquid remaining after a peritoneal washing sample is processed.
What Is Peritoneal Washing?
During a staging laparoscopy, a surgeon may place sterile fluid into the abdominal cavity and then collect it for laboratory testing. Pathologists examine the fluid for cancer cells, a process known as peritoneal washing cytology.
This testing is particularly important in gastric cancer because cancer cells can sometimes spread into the peritoneal cavity before metastatic disease becomes visible on scans. Previous research has shown that staging laparoscopy and peritoneal washings can identify disease that conventional imaging does not detect.
However, cytology has limitations. If very few cancer cells are present in the sample, the result may be negative even when microscopic peritoneal disease exists. Researchers are therefore investigating molecular techniques that might detect tumor-derived genetic material even when intact cancer cells are difficult to find.
Looking Beyond Cancer Cells
Instead of relying solely on the cells collected during peritoneal washing, the researchers investigated whether genetic material present in the liquid portion of the sample could also be analyzed using next-generation sequencing.
NGS allows laboratories to search for cancer-associated genetic alterations within DNA. Similar approaches are increasingly being studied in blood and other body fluids as forms of “liquid biopsy.”
Earlier research has demonstrated that tumor-derived DNA can sometimes be identified in ascites and peritoneal washing samples from patients with gastrointestinal cancers, although low concentrations of tumor material have historically limited the sensitivity of these tests.
By studying the peritoneal washing supernatant, the MD Anderson researchers are exploring whether molecular information that might otherwise be discarded during routine sample processing could provide another layer of information for gastric cancer staging.
Why This Matters for Patients
Determining whether gastric cancer has reached the peritoneum can significantly affect treatment discussions. Patients with microscopic or visible peritoneal disease may require a different treatment strategy than patients whose cancer appears confined to the stomach and regional lymph nodes.
More sensitive methods of detecting peritoneal disease could potentially help physicians:
identify microscopic spread that may not be visible on imaging,
better understand the extent of a patient's cancer,
avoid treatments that may be unlikely to provide benefit if metastatic disease is already present,
and guide conversations about systemic therapy, clinical trials, or specialized treatment approaches.
For patients, the study also reinforces the importance of thorough staging and evaluation by a multidisciplinary team experienced in gastric cancer and peritoneal surface malignancies.
What Patients Should Know
NGS analysis of peritoneal washing fluid is still an emerging approach and is not currently a replacement for standard staging methods, including imaging, staging laparoscopy, pathology, and conventional cytology. Additional research will be needed to determine how reliably molecular testing improves detection, which patients are most likely to benefit, and how the results should influence treatment decisions.
Still, this research points toward a future in which staging may incorporate both what pathologists can see under the microscope and what molecular testing can detect in tumor-derived DNA. For cancers that can spread microscopically within the abdomen, that added information could eventually help clinicians make more informed and individualized treatment decisions.
