Peritoneal metastasis occurs when cancer cells spread to the peritoneum, a thin membrane lining the abdominal cavity and covering many organs. This condition represents a secondary cancer, meaning it originates from a primary tumor elsewhere in the body and establishes new growths on the peritoneal surface.
What Peritoneal Metastasis Means
The peritoneum is a double-layered membrane within the abdomen. Its outer, parietal layer attaches to the abdominal and pelvic walls, while the inner, visceral layer wraps around internal organs like the stomach, liver, and intestines. This membrane secretes a small amount of lubricating fluid, which allows organs to move smoothly against each other without friction. The peritoneum also provides structural support to abdominal organs and serves as a pathway for nerves, blood vessels, and lymphatic vessels.
When cancer cells spread to the peritoneum, they retain characteristics of the original cancer. For example, colorectal cancer spread to the peritoneum is still considered metastatic colorectal cancer. This condition is often referred to as peritoneal carcinomatosis.
Peritoneal metastasis commonly originates from primary cancers within or near the abdominal cavity. Gastrointestinal cancers, such as those of the colon, rectum, stomach, appendix, and pancreas, frequently spread to the peritoneum. Colorectal tumors are associated with peritoneal spread in 5% to 10% of cases at diagnosis, with up to 50% developing later. Similarly, gastric cancers show peritoneal dissemination in about 14% of cases at initial presentation.
Gynecological cancers, particularly ovarian cancer, are also common sources of peritoneal metastasis. Ovarian cancer often spreads by cancer cells detaching from the primary tumor and circulating within the peritoneal fluid, then implanting on peritoneal surfaces and other abdominal organs. This explains why ovarian cancer is frequently diagnosed at advanced stages, as symptoms often appear only after significant abdominal spread. While less common, cancers from outside the abdomen, such as breast cancer, lung cancer, and melanoma, can also spread to the peritoneum, accounting for about 9% of cases.
Recognizing the Signs and Diagnosis
Patients with peritoneal metastasis often experience non-specific symptoms, especially in the early stages, as the condition may not cause noticeable signs until it affects a significant portion of the peritoneum. Common symptoms include abdominal pain, bloating, and distension, which can result from fluid buildup or tumor growth compressing organs. Nausea, vomiting, and changes in bowel habits like constipation can also occur due to tumor involvement of the digestive tract. Other general signs may include fatigue and unexplained weight loss or gain.
Diagnosing peritoneal metastasis involves several methods to visualize the tumors and confirm the presence of cancer cells. Imaging techniques such as CT scans, MRI, and PET scans are used to identify tumors and detect fluid accumulation (ascites) within the abdomen. These scans help determine the extent and location of the disease.
Fluid analysis, specifically paracentesis, involves collecting a sample of the ascites fluid from the abdomen. This fluid is then examined under a microscope for the presence of cancer cells, which can provide a diagnosis. A biopsy, often performed via laparoscopy, offers a more definitive diagnosis. Laparoscopy is a minimally invasive surgical procedure where a small incision is made to insert a camera, allowing direct visualization of the peritoneum and the collection of tissue samples for pathological examination. This direct visualization and tissue sampling are particularly helpful in determining the full extent of the disease and guiding treatment decisions.
How Peritoneal Metastasis Develops
The development of peritoneal metastasis often follows a “seed and soil” theory, explaining how cancer spreads to the peritoneum. In this theory, cancer cells from a primary tumor, referred to as the “seeds,” detach and travel to the peritoneum, which acts as the “soil.” The peritoneal cavity provides a favorable environment for these detached cancer cells to implant and grow.
Cancer cells can spread to the peritoneum through several routes. One common mechanism is direct extension, where the primary tumor grows through the wall of an organ and directly invades the peritoneal surface. Another way is through the shedding of cancer cells into the abdominal fluid. These cells then float within the peritoneal fluid, which naturally circulates throughout the abdominal cavity, influenced by gravity and respiratory movements.
Once these “seeds” (cancer cells) implant on the peritoneal surface, they can form new tumors. These new growths can be localized or become widespread. The ability of these cancer cells to survive in suspension within the peritoneal fluid and then adhere to and invade new sites is supported by molecular changes that promote their survival and attachment.
Treatment Options
Treating peritoneal metastasis typically involves a multidisciplinary approach, with a team of specialists collaborating to develop a comprehensive plan. This team may include surgical oncologists, medical oncologists, and other healthcare professionals. The goal of treatment is to remove as much visible cancer as possible and to target any remaining microscopic disease.
Cytoreductive Surgery (CRS)
Cytoreductive surgery (CRS) is a major surgical procedure aimed at removing all visible tumor implants from the abdominal cavity. This extensive operation, sometimes lasting eight to ten hours or more, involves excising affected portions of the peritoneum and, if necessary, parts of other organs where tumors have formed on the surface. The objective of CRS is to “debulk” the disease, leaving no macroscopic tumor behind, which is associated with improved outcomes.
Hyperthermic Intraperitoneal Chemotherapy (HIPEC)
Following CRS, hyperthermic intraperitoneal chemotherapy (HIPEC) is often performed. This specialized treatment involves circulating a heated chemotherapy solution directly within the abdominal cavity for a specified period, typically 60 to 90 minutes. The heat enhances the chemotherapy’s ability to penetrate and kill remaining cancer cells, while direct delivery minimizes systemic side effects. This combined approach of CRS and HIPEC has significantly improved survival rates for select patients with peritoneal metastasis.
Pressurized Intraperitoneal Aerosol Chemotherapy (PIPAC)
Pressurized intraperitoneal aerosol chemotherapy (PIPAC) represents a newer, minimally invasive technique for delivering chemotherapy. In PIPAC, chemotherapy drugs are administered as a fine aerosol spray into the abdominal cavity using laparoscopic instruments. This method can be used for symptom management, as a bridge to more aggressive treatments, or for patients who are not candidates for CRS and HIPEC.
Systemic Chemotherapy
Systemic chemotherapy, administered intravenously, plays an important role in targeting cancer cells throughout the body. It can be used before surgery (neoadjuvant), after surgery (adjuvant), or as the primary treatment for patients who are not candidates for surgical intervention. This approach aims to control disease progression and reduce tumor burden.
Targeted Therapy and Immunotherapy
Newer treatment strategies, such as targeted therapy and immunotherapy, are also being explored. Targeted therapies block specific pathways that cancer cells use to grow and survive, while immunotherapies boost the body’s own immune system to recognize and destroy cancer cells. These treatments are often used in combination with traditional chemotherapy or as standalone therapies, depending on the specific characteristics of the cancer.
Palliative Care
Palliative care is also an integral part of managing peritoneal metastasis, especially in advanced cases. This type of care focuses on managing symptoms, alleviating pain, and improving the patient’s overall quality of life, rather than curing the cancer. It can be provided alongside curative treatments from the time of diagnosis.