Peritoneal metastasis (PM) occurs when cancer spreads from its original site to the peritoneum, the thin membrane lining the abdominal cavity and covering most internal organs. This spread signifies an advanced stage of cancer and requires specialized treatment approaches that differ significantly from managing cancer spread in other organs. Modern therapeutic strategies, which combine aggressive surgery with localized chemotherapy, have transformed PM into a manageable, and sometimes curable, condition for carefully selected patients.
The Peritoneum and How Cancer Spreads
The peritoneum is a continuous, two-layered serous membrane composed of specialized cells called mesothelium. It forms the lining of the abdominal and pelvic cavities and wraps around the abdominal organs, creating the peritoneal cavity. This membrane secretes fluid that lubricates the organs, allowing them to glide smoothly. The complex folds of the peritoneum, such as the omentum and mesentery, also serve as conduits for blood vessels, nerves, and lymphatic tissue.
The primary mechanism for cancer spread to this area is transcoelomic dissemination, or “seeding.” This occurs when cancer cells from an organ within the abdomen grow through the organ wall. Once detached, these malignant cells shed into the peritoneal fluid and are carried throughout the cavity. The flow of the peritoneal fluid passively distributes these cells to specific anatomical locations, where they implant and grow into secondary tumors, often called peritoneal implants or nodules.
This method of spread is distinct from metastasis via the bloodstream or lymph nodes. The cells often find favorable sites for implantation in areas where the peritoneal fluid pools. The limited blood supply to the peritoneal surface also means that systemic chemotherapy delivered through the veins often struggles to reach therapeutic concentrations in the tumor nodules.
Identifying Primary Cancers and Diagnosis
Peritoneal metastasis is most frequently caused by cancers originating in or near the abdominal organs. The most common primary sites include colorectal, ovarian, gastric, appendiceal, and pancreatic cancers. PM is a considerable concern for patients with advanced ovarian, gastric, or colorectal cancer. Less commonly, cancers from outside the abdomen, such as breast or lung cancer, can also lead to peritoneal involvement.
Early symptoms of PM can be vague, often mimicking other gastrointestinal issues, which can delay diagnosis. As the disease progresses, common clinical presentations include a growing abdominal girth or distension. This distension is often caused by ascites, the buildup of fluid in the peritoneal cavity due to cancer cells irritating the membrane and disrupting fluid absorption. Patients frequently experience persistent abdominal pain, bloating, nausea, and changes in bowel habits, which can worsen into a complete bowel obstruction.
Diagnosis typically begins with cross-sectional imaging, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI). These scans identify large tumor deposits, ascites, and signs of bowel obstruction. However, small peritoneal nodules or microscopic disease are often invisible on these scans. The definitive method for confirming the diagnosis and accurately assessing the tumor burden is a diagnostic laparoscopy. This minimally invasive procedure allows the surgeon to visually inspect the entire peritoneal surface and obtain biopsies to confirm the presence of cancer cells.
Cytoreductive Surgery and Regional Therapies
For patients whose disease is confined to the abdomen and whose general health allows, the most aggressive and potentially curative treatment involves a specialized two-part procedure combining surgery and regional chemotherapy. This approach centers on Cytoreductive Surgery (CRS), a complex operation aimed at removing every visible trace of cancer from the abdominal cavity. The surgeon meticulously resects all macroscopic tumor nodules, which may involve removing sections of the peritoneum (peritonectomy), parts of affected organs, or the omentum, to achieve a complete gross resection.
The success of CRS is measured by the completeness of the cytoreduction, aiming for a score where no visible tumor deposits larger than 2.5 millimeters remain. Immediately following the surgical removal, the second phase begins: Hyperthermic Intraperitoneal Chemotherapy (HIPEC). A heated chemotherapy solution is circulated directly into the peritoneal cavity for a defined period, typically 60 to 120 minutes. The drugs are heated to around 106 to 109 degrees Fahrenheit (41 to 43 degrees Celsius), a temperature toxic to cancer cells but generally tolerated by healthy tissue.
The combination of heat and high-dose chemotherapy applied directly works synergistically to kill any remaining microscopic cancer cells. Because the drug is concentrated within the abdominal cavity, it achieves much higher local concentrations than standard intravenous chemotherapy, while systemic absorption is limited, which helps to reduce whole-body side effects. This aggressive combined procedure has significantly improved survival outcomes for selected patients with cancers originating in the appendix, colon, and ovary.
Beyond CRS and HIPEC, other localized chemotherapy techniques are utilized, often for palliative intent or when the disease extent makes CRS impossible.
Localized Chemotherapy Techniques
Pressurized Intraperitoneal Aerosol Chemotherapy (PIPAC) is a minimally invasive approach where chemotherapy drugs are administered as a pressurized aerosol, or fine mist, into the abdomen during a laparoscopy. This method is thought to improve the penetration and distribution of the drug across the peritoneal surface.
Early Postoperative Intraperitoneal Chemotherapy (EPIC) delivers non-heated chemotherapy into the abdomen through temporary catheters in the days immediately following CRS, serving as a regional follow-up treatment.
Systemic Management and Quality of Life
When the disease is too extensive, or the patient is not a candidate for a radical operation like CRS/HIPEC, systemic therapies become the primary treatment strategy. Systemic treatment involves administering drugs that travel through the bloodstream to attack cancer cells throughout the body. Traditional intravenous chemotherapy remains a foundational component of management, using agents tailored to the primary cancer type.
The landscape of systemic treatment has expanded to include targeted therapies and immunotherapy. Targeted drugs block specific molecular pathways that cancer cells use to grow and spread. Immunotherapy harnesses the patient’s own immune system to recognize and destroy the cancer cells. These systemic agents can be used alone as a palliative measure to slow disease progression, or they may be given before or after regional therapies to shrink the tumor burden or eradicate distant micrometastases.
Managing the physical complications of PM is a major focus of treatment to maintain quality of life. The development of ascites, which causes abdominal discomfort and breathing difficulties, often requires periodic therapeutic paracentesis, where a needle is used to drain the excess fluid. If the cancer causes a bowel obstruction, managing symptoms with medication or palliative surgical procedures like a bypass or stent placement can help relieve the blockage.
Palliative care is integrated early in the treatment course to focus on symptom management, emotional support, and aligning care with the patient’s goals. This specialized medical care works alongside curative treatment to address pain, fatigue, and other distressing symptoms. By providing comprehensive supportive care, the medical team maximizes comfort and ensures the highest possible quality of life at every stage of the disease.