Peritoneal carcinomatosis often spreads across the abdominal lining without forming distinct masses. Because of this, doctors usually need to combine imaging, fluid tests, and sometimes surgery, to confirm a diagnosis.
Tests
- Imaging tests. Imaging tests such as CT, MRI and PET scans are typically the first step in looking for suspected peritoneal carcinomatosis. These scans help identify visible tumor spread, fluid buildup or organ involvement. However, imaging is often not sensitive enough to detect smaller cancers or early peritoneal disease. Therefore, a negative scan does not rule out peritoneal carcinomatosis.
- Peritoneal washing cytology. In this test, fluid from the abdominal cavity is surgically collected during a minor procedure. It's then examined under a microscope. Healthcare professionals use peritoneal washing cytology to check for cancer cells floating in the peritoneal fluid. Even when no visible cancer is present, a positive cytology result is a strong sign that peritoneal spread has happened.
- Staging laparoscopy. Staging laparoscopy is a safe, minimally invasive surgical procedure used to look directly inside the abdominal cavity using a small camera. It allows healthcare professionals to inspect the peritoneum, find hidden tumors, and take tissue or fluid samples. This test is especially valuable for finding peritoneal metastases that are too small to be seen with imaging.
- Tumor marker tests. Tumor marker tests use a sample of blood to look for chemicals made by cancer cells.
- Circulating tumor DNA (ctDNA). This is a newer blood test that looks for small pieces of DNA from cancer cells in the blood. It can help find peritoneal cancer that doesn't show up on scans. However, the role of ctDNA in diagnosis is still uncertain.