context: Peritoneal cancer is a rare cancer. It develops in a thin layer of tissue that lines the abdomen. It also covers the uterus, bladder, and rectum. Made of epithelial cells, this structure is called the peritoneum. It produces a fluid that helps organs move smoothly inside the abdomen. Peritoneal cancer is not the same as intestinal or stomach cancer. Nor is it to be confused with cancers that spread (metastasize) to the peritoneum. Peritoneal cancer starts in the peritoneum, and hence is called primary peritoneal cancer. Peritoneal cancer acts and looks like ovarian cancer. This is mainly because the surface of the ovaries is made of epithelial cells, as is the peritoneum. Therefore, peritoneal cancer and a type of ovarian cancer cause similar symptoms. Doctors also treat them in much the same way. Despite its similarities with ovarian cancer, you can have peritoneal cancer even if your ovaries have been removed. Peritoneal cancer can occur anywhere in the abdominal space. It affects the surface of organs contained inside the peritoneum. The causes of peritoneal cancer are unknown. However, there are different theories about how it begins. Some believe it comes from ovarian tissue implants left in the abdomen during fetal development. Others think the peritoneum undergoes changes that make it more like the ovaries. Primary peritoneal cancer is more common in women than in men. Women at risk for ovarian cancer are also at increased risk for peritoneal cancer. This is even more likely if you have the BRCA1 and BRCA2 genetic mutations. Older age is another risk factor for peritoneal cancer. Just as with ovarian cancer, peritoneal cancer can be hard to detect in the early stages. That's because its symptoms are vague and hard to pinpoint. When clear symptoms do occur, the disease has often progressed. Then, symptoms resemble those of ovarian cancer. Many of these symptoms are due to buildup of fluid (ascites) in the abdomen. Peritoneal cancer symptoms may include: Abdominal discomfort or pain from gas, indigestion, pressure, swelling, bloating, or cramps Feeling of fullness, even after a light meal Nausea or diarrhea Constipation Frequent urination Loss of appetite Unexplained weight gain or loss Abnormal vaginal bleeding Rectal bleeding Shortness of breath In addition to asking about symptoms, your doctor will review your medical history and conduct a physical exam, which involves examining for abnormalities in these areas: Uterus Vagina Ovaries Fallopian tubes Stomach Bladder Colon and rectum Tests you may have include: Ultrasound. High-frequency sound waves produce a picture called a sonogram. CA-125 blood test. This test measures levels of a chemical in the blood called CA-125. If levels are high, peritoneal or ovarian cancer may be present. But CA-125 can be high for other reasons. So, this test cannot confirm a diagnosis of these cancers. CT scan . A computer linked to an X-ray machine produces detailed pictures of the inside the body. Lower GI series or barium enema. With this test, you first receive an enema containing a white, chalky solution called barium. This outlines the colon and rectum on an X-ray. It makes it possible to spot some tumors and other problems. Upper GI series. With this test, barium is swallowed and the esophagus, stomach, and duodenum (the first part of the small intestine) are outlined on an X-ray. Biopsy . A surgeon removes tissue by opening the abdomen during a laparotomy or by inserting tools through small holes in the abdomen (laparoscopy). If the doctor suspects cancer, he or she may remove one or more organs. A pathologist studies the tissue sample under a microscope to confirm a diagnosis of cancer. Paracentesis. In cases where surgery is not possible or ascites could be due to other causes, the doctor may instead remove fluid for examination under a microscope. This is called paracentesis. Ovarian and peritoneal cancers look the same under a microscope. So, the pattern and location of any tumors helps indicate which type of cancer is present. You may have more than one type of treatment for peritoneal cancer. The type of treatment you have depends upon: The stage and grade of the cancer The size and location of the cancer Your age and overall health Treatments for peritoneal cancer include: Surgery. Surgery not only helps with diagnosis. It may also remove any tumors. To stage and treat this cancer, a surgeon removes all visible disease. The surgeon may also remove the ovaries, fallopian tubes, and uterus as well. Depending upon what is found, the surgeon may also remove other tissue and organs. It is very important to have this surgery performed by a gynecologic oncologist. These specialists are familiar with gynecologic cancers and have greater success rates. Chemotherapy . The drugs for treating peritoneal cancer are similar to those used for ovarian cancer. You may receive these drugs by injection on an outpatient basis every one, two, or three weeks. Sometimes, chemotherapy is delivered directly into the abdomen through a catheter that was placed under the skin during surgery. This is called intraperitoneal chemotherapy. You also receive it about every three weeks, but it is a more complex treatment cycle. HIPEC (hyperthermic intraperitoneal chemotherapy). This is administration of heated chemotherapy into the peritoneum after surgery. This technique is common for peritoneal cancer that has spread from the appendix, colon, or stomach. Palliative care. Doctors often diagnose peritoneal cancer in advanced stages. Supportive care can help relieve symptoms of peritoneal cancer such as pain, weight loss, or fluid buildup. Primary peritoneal cancer prognosis is best if all cancer is removed and a gynecologic surgeon and oncologist treat you. These doctors have special knowledge of gynecologic cancers. Your doctors will closely watch you after treatment. Peritoneal cancer can spread quickly because the peritoneum is rich in lymph and blood through which it can travel. Recurrence after treatment is common with peritoneal cancer. That's because this cancer is often diagnosed in an advanced stage. You may need more than one round of chemotherapy or other surgeries. Be sure to seek support for yourself as you go through treatment and healing.