What is Peritoneal Metastasis?
The peritoneum is a large protective membrane that lines the inside of your abdomen and pelvic areas. This membrane has two connected layers: one layer, the parietal peritoneum, covers the inner surfaces of your abdominal and pelvic walls, while the second layer, the visceral peritoneum, covers the organs in your abdominopelvic cavity.
A prominent fold in the peritoneum, known as the greater omentum or the gastrocolic ligament, acts like a security guard for your abdomen. Its role is to contain inflammation and limit the spread of infection or localized disease within your abdominopelvic cavity. However, this can also make it vulnerable to involvement in any abdominal cancers, as the disease can spread locally.
‘Peritoneal carcinomatosis’ (PC) is a term that describes the spread of cancer to the peritoneum. This was first named in 1931 by Sampson, specifically for describing the spread of ovarian cancer cells to the peritoneum. Now, the term is used to describe almost all cancer that has spread to the peritoneum. That being said, it’s more common for cancer to spread to the peritoneum from somewhere else in the body rather than starting there. This spread often occurs with advanced gastrointestinal or gynecological cancers.
Historically, if cancer had spread to the peritoneum, this was considered incurable and fatal. It was at a point where surgical treatment to cure the disease was deemed unreasonable. However, in more recent years, advancements in surgical techniques and medical management strategies have greatly altered the course of the disease. Nowadays, it’s possible to effectively treat this condition, which has greatly improved the likelihood of patients living without signs of the disease and increased overall survival rates.
What Causes Peritoneal Metastasis?
Peritoneal involvement, which refers to the spread of cancer to the lining of the abdomen, is most commonly associated with cancers of the digestive, reproductive, and urinary systems. It’s particularly prevalent in cases of ovarian, colon, and stomach cancers that have advanced to later stages. Other less common sources of this type of cancer spread may include cancers of the pancreas, appendix, small intestine, uterus, and prostate.
It’s rare but not impossible for cancers that originated outside the abdominal area to also lead to peritoneal involvement, which account for around 10% of such cases. The most common among these are breast cancer, lung cancer, and malignant melanoma – a severe type of skin cancer. Lung cancer is especially significant, given the high global incidence of this type of cancer. Even though peritoneal spread is rare in lung cancer, the overall high number of cases means it could still contribute significantly to the total number of peritoneal involvement cases worldwide.
Ovarian cancer is the most common disease leading to peritoneal involvement, occurring in 46% of cases. This is largely due to how close the ovaries are to the abdominal lining, and the cellular similarities between them.
Additionally, colorectal cancer contributes to a substantial number of patients with peritoneal involvement due in part to the overall high number of these cancers. About 7% of these cases develop synchronous peritoneal metastasis, meaning the cancer spreads to the peritoneal area at the same time it is developing elsewhere. Non-hormone related pancreatic cancer can present with peritoneal involvement in about 9% of cases, and stomach cancer, often detected at more advanced stages, can have a peritoneal spread in about 14% of cases. Slow-growing neuroendocrine tumors originating from the digestive tract can also spread to the abdominal lining, a scenario seen in about 6% of such cases, with frequency increasing with age.
Finally, there are cases where it’s hard to pinpoint where the cancer that has spread to the abdominal lining originally started. In these scenarios, which account for 3 to 5% of cases, we refer to it as peritoneal involvement with an unknown primary source.
Risk Factors and Frequency for Peritoneal Metastasis
Peritoneal metastasis, also known as PM, is a rare condition where cancer cells spread and grow in the lining of the abdomen (the peritoneum). Since preoperative detection and imaging methods aren’t very effective, we don’t have exact data about how many people are affected by it. However, statistics from the past two decades suggest that the number of people with peritoneal cancer is increasing, which could be due to advancements in our medical technology and our ability to manage the disease. Interestingly, only 3% of peritoneal metastasis actually originates from the peritoneum itself. Most often, it’s due to cancer spreading from other parts of the body.
- One large study from Ireland showed that the number of people diagnosed with peritoneal metastasis went up from 228 in 1994 to 402 in 2012.
- In most cases, the patients were female and 70% of them were 60 years old or more at the time they were diagnosed.
Cancer of different types can lead to peritoneal metastasis, and the incidence rates can differ. In the U.S., colorectal cancer can often lead to this condition. About 5 to 8% of all colorectal cancer patients will develop peritoneal metastasis. This roughly translates to 2 to 3 individuals per 100,000 people per year.
Neuroendocrine tumors of the gastrointestinal (GI) tract, another type of cancer, cause peritoneal metastasis at a rate of about 1.6 per 1 million people per year in the U.S.
Signs and Symptoms of Peritoneal Metastasis
Peritoneal metastasis, or cancer spreading to the lining of the abdomen, is usually discovered in the late stages of the disease. Symptoms of this condition often align with those of advanced cancer. It is frequently detected unexpectedly during surgeries to remove the original, or primary, tumor
Two significant indicators of peritoneal metastasis are ascites (fluid buildup in the abdomen) and bowel obstruction. However, these signs are found in less than half of the patients. Like any form of cancer, affected individuals may also experience symptoms like loss of appetite, abdominal discomfort, nausea, vomiting, constipation, bloating, and weight loss. Notably, two particular factors that might suggest peritoneal metastasis include presence of cancer cells in the abdominal fluid (seen in 28% to 30% of colorectal peritoneal metastasis patients) and bowel obstruction (noted in 8% to 20% of colorectal peritoneal metastasis patients).
Due, in part, to these varied and non-specific symptoms, diagnosing peritoneal metastasis based on clinical presentation alone is challenging. However, when any evidence of abdominal cancer arises, healthcare providers should be cognizant of potential late-stage disease, such as peritoneal metastasis — even if imaging tests don’t immediately reveal it. Examination of the peritoneum (abdominal lining) and any fluid in the abdomen can be conducted during scheduled or emergency procedures.
Testing for Peritoneal Metastasis
If you have cancer that has spread to the lining of your abdominal cavity (known as metastatic peritoneal cancer), it’s often discovered by accident during surgery or during a diagnostic medical scan like a CT scan or MRI that was ordered for another reason. To confirm the type of cancer and distinguish it from a primary peritoneal cancer, doctors usually take a biopsy – a small sample of tissue from the tumor or lesion. Ideally, the testing that doctors do should:
1. Detect any sign of potential peritoneal metastasis early, in patients who have recently been diagnosed with a cancer of the abdomen or pelvic region. This allows any extra-abdominal areas (parts outside the abdominal cavity) with cancer spread to be identified, which would make surgery with the intention to cure, impossible.
The aim is also to understand the scope, size, and impact of the cancer on major organs. This helps to select the patients correctly for a procedure known as cytoreductive surgery (CRS), often partnered with warm chemotherapy given directly into the abdomen (technically called hyperthermic intraperitoneal chemotherapy (HIPEC)). The staging of Peritoneal Carcinomatosis (PC) – the spread of cancer on the peritoneal surface – can give valuable information about probable results and the prediction of survival following treatment.
Cancerous growths involving the peritoneum can sometimes be seen with CT scans, MRIs, or PET/CT scans that use a radioactive drug. The suitability of these scans depends on the type of cancer and where it is. The Peritoneal Carcinomatosis Index (PCI) is a scoring system that’s useful for selecting patients for surgery, and offers a better understanding of possible outcomes. Therefore, most scans are aimed at providing an accurate PCI score.
With a CT scan, certain features can suggest peritoneal metastasis, such as thickening of the folds of tissue in the abdominal cavity or unusual structures that could suggest a cancer spread. Sometimes you can see a thick, uneven layer called an “omental cake,” this is a layer of cancer tissue. While a CT scan can pick up nodules if they are on the surface of the liver or spleen, and can detect a buildup of fluid in your abdomen, if there’s over 50 ml, it is not always the most reliable at detecting peritoneal tumors for future treatment decisions.
MRI is another tool that can help to detect peritoneal metastasis, but it hasn’t been proven significantly better than CT scanning. A PET/CT scan, which involves a CT scan and a PET scan (which uses a radioactive drug to show cell activity), can be better at showing the precise location and area of the spread. This scan is especially useful in tracking the response to treatment over the long term.
Laparoscopy, a type of keyhole surgery where a camera is passed through a small incision, can be recommended for assessing whether the peritoneal nodules can be removed before starting cytoreductive surgery (CRS). This can be particularly useful in situations where previous imaging tests have not supplied enough information about the spread and extent of the disease. Despite fears of triggering tumor growth at the site of the keyhole surgery, many surgeons find it useful for making decisions about treatment.
New diagnostic techniques have also been proposed. Some groups have suggested that checking fluid in the abdomen for a specific protein could be helpful for diagnosing bowel cancer with peritoneal metastasis. CT scan that includes the small bowel (CT-enteroclysis) is particularly useful in detecting cancerous growths in the small bowel and surrounding tissues. Flexible endoscopy, a procedure that uses a bendy tube to see inside your body, is also being explored as a method of checking the extent of disease before surgery. Hopefully, future studies will confirm the usefulness of these new methods.
Treatment Options for Peritoneal Metastasis
The aggressive treatment of peritoneal carcinomatosis (PC), a form of cancer that spreads throughout the lining of the abdomen, has become more common due to improvements in surgical techniques and the positive results related to targeted chemotherapy. A treatment plan that combines complete cytoreductive surgery (CRS), a procedure aimed at removing all visible cancer, and hyperthermic intraperitoneal chemotherapy (HIPEC), a type of chemotherapy heated and directly delivered into the abdomen, has become a key strategy for treating PC from most gastrointestinal and genitourinary tracts carcinomas (cancers that develop in the organs of the digestive and urinary system).
This treatment approach, which demonstrated effective results in a clinical trial in 2003, emphasizes total cytoreductive surgery as a major factor for predicting the survival outlook, with survival rates up to 45% if CRS is complete, compared to under 10% when the surgery is incomplete. The aggressive surgical approach of CRS was promoted by Dr. Sugarbaker due to its positive survival benefits.
Choosing the right patients for surgery is an integral first step in the treatment process. Factors such as age, overall health condition, and whether the patient can withstand the physical toll of surgery are all considered. It’s also important to ensure that the cancer has not spread to other parts of the body. Imaging techniques such as CT, MRI or PET/CT scans, depending on the type of cancer, are used to check for possible areas of cancer spread such as the chest, spine bones, brain, etc.
As for the extend of the peritoneal cancer, CT/MRI are used to determine the size, degree, and type of lesions in the peritoneum. A scoring system, known as the Peritoneal Cancer Index (PCI), is used to determine the feasibility of surgery and to predict the likely prognosis. A high PCI score which might indicate involvement of the small bowel, for example, could suggest a poor prognosis.
After determining a patient’s fitness for surgery, CRS and HIPEC are usually performed. The goal is to remove all visible cancer through surgical resections. But since it’s hard to completely eliminate cancer cells in PC, the idea is to remove any visible lesions and rely on HIPEC to potentially remove cancer cells that can’t be seen. This approach has improved survival and quality of life in patients.
In addition to CRS and HIPEC, Pressurized Intraperitoneal Aerosol Chemotherapy (PIPAC) is a new, innovative treatment that may be beneficial in patients with extensive PC who are not suitable or unfit for surgery. The technique involves applying chemotherapy drugs in an aerosol form under pressure into the abdomen, which could potentially lead to better penetration into the tissue and more effective distribution. This method is also thought to be better at reducing tumor size compared to traditional chemotherapy or systemic chemotherapy.
What else can Peritoneal Metastasis be?
When a doctor is trying to diagnose peritoneal metastasis, they usually consider other diseases that have similar symptoms. These include:
- Primary peritoneal malignancy (cancer that originates from the peritoneum itself)
- Peritoneal mesothelioma (a rare type of cancer that affects the tissue covering abdominal organs)
- Peritoneal tuberculosis (a form of tuberculosis that affects the peritoneum)
- Peritonitis (inflammation of the peritoneum, usually because of an infection)
What to expect with Peritoneal Metastasis
There are several factors currently used to predict the outcome (prognosis) for individuals with peritoneal carcinomatosis, a condition where cancer has spread to the lining of the abdominal cavity:
1. The type of cancer cells (tumor histology)
2. Evaluating how far the disease has spread during surgery (intraoperative assessment)
3. Scoring systems used during surgery that evaluate the spread of cancer, including Gilly staging, PCI scoring, Japanese cancer society staging for stomach cancer, and the Dutch Simplified Peritoneal Carcinomatosis Index (SPCI).
4. Effectiveness of removal of visible tumors during surgery (completeness of cytoreduction or CC)
5. Patient’s observable health complaints (clinical symptoms)
Key health outcomes like overall survival, being disease-free, and 5-year survival rate, are influenced by factors such as the type of initial cancer, how effective the surgery was in removing tumors (based on CC scoring), treatment with heated chemotherapy in the abdomen (HIPEC treatment), and the natural progress of the cancer.
If the original source of cancer (primary tumor) is unknown (UPT), the prognosis tends to be poor – survival can be as short as three months. Though certain types of cancer cells have shown favorable survival, it’s important to aim at discovering and identifying the original source of cancer, as this may improve the outcome of the treatment.
Possible Complications When Diagnosed with Peritoneal Metastasis
Complications associated with untreated or inoperable peritoneal carcinomatosis (PC) can include:
- Refractory ascites or buildup of fluid
- Intestinal obstruction, or blockage in the intestines
- Dysfunctional digestion and absorption of food in the gastrointestinal (GI) tract
- Pulmonary thromboembolism, or a clot in the lungs
- Peritonitis, or inflammation of the inner lining of the stomach
- Complications from high blood pressure in the liver’s portal system, which may lead to upper GI bleeding, an enlarged spleen, altered brain function, and ascites
- Enteric fistula, or an abnormal passage in the GI tract
Postoperative complications related to CRS (tumor removal surgery) can include bleeding, infection, blockage of the bowel, hemorrhage, or peritonitis.
Complications associated with HIPEC (a type of chemotherapy) may include:
- Oxaliplatin, which is mixed with sugar solutions, can potentially cause postoperative acidosis (high acid levels in the blood) and high blood sugar
- Mitomycin C may result in a low white blood cell count (neutropenia) affecting about one-third of patients and other gastrointestinal side effects
Preventing Peritoneal Metastasis
Metastasis in the peritoneum, or the lining of the abdomen, is a big challenge for patients. Therefore, it’s important that medical staff explain the situation clearly to them. If required, patients may be referred to a psychologist for additional support. In addition, a condition known as third spacing can cause fluid buildup in the abdomen, known as ascites. This can be managed by reducing salt and water intake.
