Peritoneal mesothelioma is a rare and aggressive cancer that affects the lining of the abdomen, known as the peritoneum. Although they’ve historically been treated the same way, there are many differences between peritoneal mesothelioma and pleural mesothelioma, the more common form of the mesothelioma that is found in the lining of the lungs. Because peritoneal mesothelioma symptoms are often subtle, the disease has often spread by the time it is diagnosed.
We spoke with gastrointestinal medical oncologist Kanwal Raghav, M.D., to learn what sets this rare cancer apart and progress in treating the disease.
How rare is peritoneal mesothelioma?
About 3,000 new cases of mesothelioma are diagnosed each year in the U.S., and only about 300 to 500 of these are peritoneal mesothelioma. Here at MD Anderson, we have a fairly large program for peritoneal mesothelioma and see about 50 to 60 new patients a year.
Who is at risk for peritoneal mesothelioma?
Asbestos exposure is commonly associated with mesothelioma because it’s the main risk for pleural mesothelioma, and is seen in about 80% to 90% of cases when mesothelioma develops in the lining of the lungs. But in peritoneal mesothelioma, asbestos is only associated with about 30% to 40% of cases. This means we don’t know what causes the disease in a large number of patients. Exposure to asbestos is definitely a risk factor, but beyond that, there are a lot of unknowns.
Peritoneal mesothelioma is also more common in women. That is the opposite of what we see in pleural mesothelioma, where men are more commonly affected.
What are the most common symptoms of peritoneal mesothelioma, and how is it diagnosed?
Peritoneal mesothelioma doesn’t cause symptoms in many patients until the disease is advanced. Signs to watch out for include abdominal pain or swelling, nausea, altered bowel movements, unexplained fever and unexplained weight loss. A biopsy is required to diagnose peritoneal mesothelioma.
How is peritoneal mesothelioma typically treated?
Traditionally, peritoneal mesothelioma has been treated the same way as pleural mesothelioma. In fact, there aren’t cancer treatment guidelines specifically for peritoneal mesothelioma. Many patients undergo cytoreductive surgery, followed by hyperthermic intraoperative peritoneal perfusion with chemotherapy (HIPEC), a procedure where heated chemotherapy is pumped into the patient’s abdominal cavity. When surgery is not curative, the standard of care is platinum chemotherapy, sometimes followed by a second- or third-line chemotherapy, if needed.
Has there been any progress in treating peritoneal mesothelioma?
One of the difficulties in treating peritoneal mesothelioma is that drugs haven’t been studied specifically for this disease. The standard treatments are based on studies done in pleural mesothelioma patients. Some Phase I clinical trials allow patients with peritoneal mesothelioma to enroll, but it’s difficult to draw conclusions without dedicated research for this rare cancer type.
We just published results from the first Phase II study with a cohort specifically designed to test an immunotherapy and targeted therapy combination for treatment of advanced peritoneal mesothelioma. The results were encouraging, showing the treatment combination was safe and produced a positive response in 40% of enrolled patients.
It was also the first clinical trial for peritoneal mesothelioma that used biopsies before and during treatment to better understand the disease and look for potential biomarkers for response to immunotherapy. A biomarker is a biological molecule, such a specific protein or gene expression, that’s found by analyzing the tumor through a biopsy. When you’re doing a clinical trial for a rare cancer like this, it’s so important to maximize the information from the study. We showed that it’s feasible to do a study that requires patients to undergo multiple biopsies to look for biomarkers before and during treatment in this rare population. Our patients not only got the benefit of receiving an effective therapy, but were also very supportive of and willing to participate in this research.
The next step is to do a larger clinical trial and to see if this treatment combination could be effective for newly diagnosed patients and others prior to surgery.
What else do you want patients and caregivers facing a peritoneal mesothelioma diagnosis to know?
We are working tirelessly to build clinical trials for peritoneal mesothelioma. Clinical trials, especially for rare cancers like this, would not be possible without the support of our patients and their caregivers. I encourage patients with peritoneal mesothelioma to seek out a cancer center with clinical trials early in their treatment so that we can learn more about this disease and make progress.