You’ve seen the commercials. But what exactly is this rare form of cancer?
Me-so-the-li-o-ma. You’ve probably heard this mouthful of a word—the name of a rare cancer—on late night television commercials. Or maybe you’ve heard that mesothelioma is linked to working with asbestos, but that’s the extent of your knowledge. To shed some light on this rare condition, HealthLeader enlisted the help of oncologist Jorge Quesada, MD, a visiting associate professor at The University of Texas Health Science Center at Houston (UTHealth) Medical School.
What is mesothelioma? Mesothelioma is cancer of the mesothelium—a thin membrane lining the lungs, stomach, heart and other organs. The most common form of mesothelioma is pleural mesothelioma. In pleural mesothelioma, cancer cells grow on the pleura—the sac that lines the chest cavity and protects the lungs. Continued exposure to asbestos, over a period of many years, is the most frequent cause of the disease.
Only about 2,000 to 3,000 new cases of mesothelioma are diagnosed each year in the United States, according to the American Lung Association.
“It continues to be a relatively rare condition,” Quesada says. “You don’t get to see too many cases in private practice, perhaps three to four cases a year. The number of cases varies according to geographic location and demographics.”
What is asbestos? Asbestos is a fibrous mineral that is resistant to heat, fire and chemicals and does not conduct electricity. Until regulations passed in the ’70s and ’80s restricted its use, asbestos was widely used to insulate homes, and in the ship building and automotive industries. When inhaled, asbestos fibers may enter the lungs and penetrate and irritate the cells in the pleura. Continual irritation may lead to mesothelioma.
Who gets the disease? Most people who develop mesothelioma have worked with asbestos for many years. Because mesothelioma can take up to 30 to 50 years to develop, the majority of patients with the disease are over age 65. A notable exception may be the first responders to the 9/11 attack on the World Trade Center, who were exposed to massive amounts of asbestos in a short period of time.
“There is an increased risk of mesothelioma with the amount and length of exposure,” Quesada says. People who worked in an asbestos-filled environment for a week or so (with the potential exception of first responders to the 9/11 attack) are at minimal risk for developing mesothelioma, because it takes years of cumulative exposure for it to develop, in most cases.
“Over the past few decades, we have seen a decline in mesothelioma because of improved regulations in asbestos used for construction and in factories,” Quesada continues. The disease is more common in other places in the world, he says, particularly in China, which has seen a rapid increase of industrialization coupled with less stringent regulation of asbestos.
Can mesothelioma be caused by things other than working with asbestos? Possibly, but 70 to 80 percent of people who get mesothelioma have been heavily exposed to asbestos at work, according to the American Lung Association. Scientists are researching how asbestos fibers change the mesothelial cells of the lungs and cause cancer. Research is also under way to clarify if the virus SV40—a DNA virus that has the potential to cause tumors—has any role in causing mesothelioma. SV40 has been linked to mesothelioma in some studies, but its role remains controversial and debatable, Quesada says.
What are the symptoms of mesothelioma? Common symptoms of mesothelioma include shortness of breath, pain under the rib cage and coughing. Unfortunately, these symptoms are also found in other minor, non-life threatening conditions affecting the chest and lungs such as the flu, bronchitis and pneumonia. As a result, mesothelioma is often overlooked until the cancer is advanced. Depending on the stage of the cancer, other symptoms may include weight loss, fluid in the chest, loss of appetite and trouble swallowing.
How is the disease diagnosed? After a complete physical exam and health history, doctors who suspect mesothelioma will order a series of tests to rule out more common causes of symptoms, including benign and malignant conditions (lung cancer). Tests may include chest x-rays and other imaging studies to look for abnormal findings. “Ultimately, the diagnosis can only be confirmed by obtaining biopsies of the pleura or finding malignant cells in pleural fluid,” Quesada says.
What is the prognosis like for someone with mesothelioma? Because of the silent nature of this disease, mesothelioma is often diagnosed when the cancer is at an advanced stage. Average survival time is only about one year, according to the American Lung Association. Five-year survival rates are slowly improving, and scientists are constantly searching for new treatments.
“When it (mesothelioma) develops, it develops slowly and without very specific signs,” Quesada says. “And it is difficult to diagnose. The symptoms are not very obvious, and by the time it is diagnosed, the tumor has often spread across a large area.”
What are current treatments for mesothelioma? “The best possible treatment is early intervention, and surgical intervention,” Quesada says, adding that the surgeon should be an experienced oncology surgeon who is part of a physician team including an oncologist. He recommends patients diagnosed with mesothelioma choose a cancer center that treats a large number of patients with the disease.
Even with a skilled surgeon, mortality for the surgery remains high. “An estimated 15 to 20 percent of patients may die of complications,” Quesada says.
And surgery is not an option for many patients with the disease, Quesada says, because they are older and may also smoke, have emphysema and heart conditions that make them ineligible for surgery.
Other treatment options for mesothelioma may include a combination of chemotherapy, radiation and targeted drugs. For patients in advanced stages of the disease, palliative therapy helps reduce pain and discomfort caused by the disease.
What research is being done on mesothelioma? “Oncology is undergoing a transformation,” Quesada says. “Researchers are now identifying molecular pathways that may help with cancer intervention.”
New drugs for mesothelioma target those molecular pathways that cause cell changes, and may have fewer side effects than traditional, broad-based chemotherapy agents. One group of these new drugs is angiogenesis inhibitors, which block formation of blood vessels that feed tumors. Other drugs target different changes in the cell. Researchers are conducting clinical trials using drugs used for other types of cancer, including imatinib (Gleevec), dasatinib (Sprycel), bortezomib (Velcade), and vorinostat (Zolinza).
“We are cautiously optimistic about finding an agent that may help,” Quesada says. “Ongoing trials may hopefully lead to new options for patients with mesothelioma. In conjunction with chemotherapy, these new drugs will be a good option for patients who are not candidates for surgery.”
Other new therapies for mesothelioma under investigation include gene therapy, cancer vaccines and photodynamic therapy. The effectiveness of multimodality therapy—a combination of surgery, chemotherapy and radiation therapy—is also being tested.
What else should readers know about mesothelioma? People who have been exposed to asbestos should quit smoking to lower their risk for developing the disease, and see a doctor for regular checkups.
“Early diagnosis is the key to helping patients,” Quesada says, adding that patients who worked with asbestos should volunteer that fact to their doctor. “Bring information about exposure up front; don’t wait for the nurse or doctor to ask.”