Peritoneal carcinomatosis is the spread of cancer to the peritoneum, the thin membrane that lines the inside of your abdomen and covers most of your abdominal organs. It is the most common malignant process affecting the peritoneal cavity and typically develops as a secondary spread from cancers that originate elsewhere, most often in the colon, rectum, stomach, or ovaries. Without treatment, median survival has historically been measured in months, but newer surgical and chemotherapy approaches have significantly improved outcomes for selected patients.
How Cancer Spreads to the Peritoneum
Cancer cells reach the peritoneum through a process called intraperitoneal seeding. Cells detach from the original tumor, enter the peritoneal fluid that naturally circulates inside the abdomen, travel to distant areas of the peritoneal lining, attach to it, and then invade the tissue beneath. The movement of these loose cancer cells is driven by two forces: the normal wave-like contractions of the gut (peristalsis) that push peritoneal fluid around, and simple gravity pulling cells downward into the pelvis and lower abdomen.
This pattern of spread is especially characteristic of ovarian cancer and a condition called pseudomyxoma peritonei, where mucus-producing tumors coat the peritoneal surface. But any cancer that starts in or near the abdominal cavity can seed the peritoneum if cells break free from the primary tumor.
Which Cancers Cause It Most Often
Ovarian and gastrointestinal cancers have the highest tendency to spread to the peritoneum. Among gastrointestinal cancers, colorectal and gastric (stomach) cancers are the most frequent sources. Appendiceal cancers, while rarer, also have a well-known association with peritoneal disease. Pancreatic cancer can spread to the peritoneum as well, though it tends to carry a particularly poor prognosis when it does.
Peritoneal carcinomatosis can also, less commonly, originate as a primary cancer of the peritoneum itself, called primary peritoneal carcinoma. This behaves similarly to advanced ovarian cancer and is treated along the same lines.
Symptoms and How It Feels
Early peritoneal carcinomatosis often produces no noticeable symptoms, which is one reason it tends to be diagnosed at an advanced stage. As cancer deposits grow across the peritoneal surface, the most common development is malignant ascites, a buildup of fluid in the abdomen. You may notice your belly becoming swollen or feeling tight, clothes fitting differently around your waist, or a sense of fullness even after eating very little.
Other symptoms develop as the disease progresses. Abdominal pain or cramping can result from tumor deposits pressing on organs or pulling on the peritoneal lining. Nausea, loss of appetite, and unexplained weight loss are common. If cancer deposits grow large enough to compress or block the intestines, you may experience worsening nausea, vomiting, inability to pass gas or stool, and escalating abdominal pain. This complication, called malignant bowel obstruction, is one of the most serious consequences of advanced peritoneal disease.
How It Is Diagnosed
Contrast-enhanced CT scanning is the first-line imaging tool, with reported sensitivity ranging from 25% to 100% depending on the size and location of tumor deposits. The challenge is small nodules: deposits under 5 mm, particularly those on the small bowel surface, in the root of the mesentery, or under the diaphragm, drop CT detection rates to as low as 11% to 48%.
MRI outperforms CT for these hard-to-spot deposits. Specialized MRI techniques using fat suppression and contrast enhancement can detect nodules smaller than 5 mm, including those in anatomically difficult locations. PET scanning, which detects metabolically active cancer cells, has shown sensitivities of 78% to 97% for peritoneal disease originating from ovarian cancer, making it a useful complement to CT.
When imaging is inconclusive, diagnostic laparoscopy (inserting a small camera through a keyhole incision) allows surgeons to directly visualize the peritoneal surfaces. During this procedure, surgeons often calculate a Peritoneal Cancer Index, or PCI, score. This scoring system divides the abdomen into regions and grades the size of tumor deposits in each one, producing a number from 0 to 39. The PCI score helps determine whether curative surgery is feasible. For colorectal cancers, a PCI below 20 is generally considered operable. For ovarian cancers, the traditional threshold has been a PCI below 25, though more recent data suggests a PCI below 17 may better predict whether surgeons can remove all visible disease.
Surgery Combined With Heated Chemotherapy
The most aggressive treatment option is cytoreductive surgery (CRS) followed by hyperthermic intraperitoneal chemotherapy, commonly known as HIPEC. This is a two-part procedure done during the same operation.
In the first phase, surgeons work to remove every visible trace of cancer from the peritoneal cavity. This often means stripping away portions of the peritoneal lining itself, along with sections of affected organs. Complete removal of all visible cancer is the single most important factor in determining outcomes. If surgeons cannot achieve this, the benefit of the procedure drops significantly.
Once the surgical removal is complete, the second phase begins. Chemotherapy drugs are dissolved in a heated fluid (kept between 41 and 43 degrees Celsius, roughly 106 to 109 degrees Fahrenheit) and circulated throughout the open abdominal cavity for 30 minutes to an hour. The heat serves two purposes: it helps the chemotherapy penetrate deeper into any remaining microscopic cancer cells, and it has a direct cell-killing effect of its own. The entire operation is a major procedure, typically lasting many hours, with a recovery period of several weeks.
Systemic Chemotherapy and Newer Approaches
Not everyone is a candidate for CRS and HIPEC. When the disease is too widespread, when the patient’s overall health makes major surgery too risky, or when the cancer has spread beyond the peritoneum, systemic (whole-body) chemotherapy is the standard approach. Updated consensus guidelines for colorectal cancer with peritoneal spread now favor starting with systemic chemotherapy before considering surgery, rather than rushing to operate upfront. Early referral to a center specializing in peritoneal surface cancers is recommended regardless of the initial treatment plan.
A newer option called pressurized intraperitoneal aerosol chemotherapy, or PIPAC, is available for patients who cannot undergo curative surgery or whose cancer has progressed despite standard treatment. During a short laparoscopic procedure, chemotherapy is delivered as a pressurized mist directly into the abdomen. Unlike HIPEC, PIPAC does not involve removing any cancer tissue and is considered palliative, meaning it aims to control symptoms and slow disease rather than cure it. Treatments are repeated every six to eight weeks alongside systemic chemotherapy. Compared to systemic chemotherapy alone, adding PIPAC has been associated with fewer and shorter hospitalizations, longer survival, and improved quality of life.
Prognosis by Cancer Type
Survival varies dramatically depending on the origin of the cancer and whether curative surgery is possible. Without aggressive surgical treatment, historical data paints a sobering picture. A large European multicenter study found median survival of 6.9 months for colorectal peritoneal carcinomatosis and 6.5 months for gastric origin. Pancreatic cancer with peritoneal spread carried a median survival of just 0.7 months in one series.
CRS with HIPEC has changed these numbers substantially for selected patients. In colorectal peritoneal carcinomatosis, five-year survival rates after complete cytoreduction now reach into the 30% to 50% range at experienced centers, a dramatic improvement over chemotherapy alone. Appendiceal cancers, particularly low-grade types, tend to have the most favorable outcomes after CRS and HIPEC. Gastric cancer with peritoneal spread generally carries a worse prognosis even with aggressive treatment, though outcomes are improving.
The PCI score at the time of surgery is one of the strongest predictors. Lower scores, meaning less widespread disease, correlate with better survival. Achieving complete removal of all visible tumor during surgery is equally critical. When even small amounts of residual cancer are left behind, long-term outcomes decline sharply.
Managing Bowel Obstruction
Malignant bowel obstruction is one of the most difficult complications of advanced peritoneal carcinomatosis. When cancer deposits block the intestines, the priority shifts to controlling symptoms and restoring comfort. If the blockage occurs at a single point, a metal stent (a small expandable tube) can sometimes be placed through an endoscope to reopen the passage without major surgery. Palliative surgery to bypass or remove the obstruction is sometimes considered but is not routinely performed because outcomes in advanced disease are unpredictable.
When neither stenting nor surgery is possible, a combination of medications can effectively manage symptoms. This typically includes strong pain relievers, anti-nausea drugs, medications to reduce the volume of intestinal fluid, and steroids to decrease inflammation and swelling inside the bowel. Steroids in particular can sometimes resolve the obstruction entirely by reducing the swelling around tumor deposits. For patients who cannot control vomiting through medication alone, a small tube placed through the skin into the stomach can provide relief by draining fluid and gas, avoiding the discomfort of a tube through the nose.