Malignant mesothelioma is a cancer that develops in the thin tissue lining several of the body’s internal organs, most commonly the lungs. It is strongly linked to asbestos exposure, often appearing decades after the initial contact. About 81% of cases originate in the tissue surrounding the lungs (the pleura), making pleural mesothelioma by far the most common form.
How Asbestos Causes Mesothelioma
The mesothelium is a protective membrane that lines the chest cavity, abdominal cavity, heart, and other organs. When asbestos fibers are inhaled, the thinnest ones (longer than 5 micrometers) can penetrate through lung tissue and reach the pleural space surrounding the lungs. Once there, the fibers cause damage through two main pathways.
First, the body’s immune cells attempt to engulf the fibers but can’t fully break them down. This process generates highly reactive molecules called free radicals, which directly damage DNA inside mesothelial cells. The result is genetic mutations that can push cells toward uncontrolled growth. Second, asbestos fibers physically interfere with cell division by tearing or puncturing the internal structures cells use to split in two, leading to chromosomal abnormalities.
Neither of these events is a one-time occurrence. Asbestos fibers persist in tissue indefinitely, creating a repeating cycle of cell damage, inflammation, and repair. As damaged mesothelial cells die, they release signaling molecules that sustain chronic inflammation and create an environment that favors tumor growth. Over years and decades, this ongoing damage accumulates until normal cells transform into cancerous ones.
The Long Gap Between Exposure and Diagnosis
One of the most striking features of mesothelioma is its latency period. The median time between first asbestos exposure and a pleural mesothelioma diagnosis is about 38 years. While rare cases have developed in under 10 years, 44% of pleural cases and 54% of peritoneal (abdominal) cases appear 40 or more years after initial exposure. This means someone exposed to asbestos in the 1980s could receive a diagnosis today, long after forgetting the exposure ever happened.
Occupational exposure accounts for the majority of cases. Construction workers, shipyard workers, miners, insulation installers, and military personnel (particularly Navy veterans) have historically faced the highest risk. However, secondary exposure is also documented: family members who inhaled fibers carried home on a worker’s clothing have developed the disease.
Where Mesothelioma Develops
Mesothelioma is classified by where in the body it forms. According to CDC data covering 2003 to 2022 in the United States:
- Pleural (lungs): 81% of cases. This is the form most people are referring to when they say “mesothelioma.”
- Peritoneal (abdomen): 11.1% of cases. This develops in the lining of the abdominal cavity.
- Pericardial (heart): 0.2% of cases. Extremely rare, forming in the tissue surrounding the heart.
- Tunica vaginalis (testicles): 0.2% of cases. The rarest recognized form.
Cell Types and Why They Matter
Beyond location, mesothelioma is also classified by its cell type under a microscope. This distinction directly affects how aggressive the cancer is and how well it responds to treatment.
Epithelioid mesothelioma makes up roughly 55% of cases. These tumors consist of rounded, cohesive cells and tend to grow more slowly than other types, generally carrying the best prognosis. Sarcomatoid mesothelioma accounts for only about 10% of cases. Its cells are elongated and grow in disorganized patterns resembling a type of soft tissue cancer, making it the most aggressive and hardest to treat. Biphasic mesothelioma, around 20% of cases, contains a mix of both cell types. A tumor needs at least 10% of each component to qualify as biphasic, and prognosis depends heavily on which cell type dominates.
Symptoms and How It’s Diagnosed
Pleural mesothelioma commonly presents with shortness of breath, chest pain, persistent cough, and unexplained weight loss. Peritoneal mesothelioma tends to cause abdominal swelling, pain, and digestive changes. Because these symptoms overlap with many common conditions, and because the disease is relatively rare, misdiagnosis or delayed diagnosis is frequent.
Imaging scans such as CT or PET scans can reveal suspicious thickening of the pleural lining or fluid buildup, but a tissue biopsy is required for a definitive diagnosis. Pathologists examine the biopsy sample using specialized staining techniques to distinguish mesothelioma from other cancers that can spread to the same areas. Blood tests measuring a protein called mesothelin (the only FDA-approved biomarker for this cancer) can support the diagnosis, though they aren’t reliable enough to be used alone.
Survival Rates
Mesothelioma carries a difficult prognosis. Five-year survival rates for pleural mesothelioma, based on diagnoses from 2015 to 2021, are 23% when the cancer is still localized, 15% when it has spread to nearby tissues (regional), and 11% when it has reached distant parts of the body. Because symptoms typically don’t appear until the disease is advanced, most diagnoses fall into the regional or distant categories.
Treatment Approaches
Treatment for mesothelioma typically involves a combination of therapies rather than any single approach. The specific plan depends on the cancer’s stage, cell type, and location, as well as the patient’s overall health.
Surgery
For pleural mesothelioma caught at an operable stage, two main surgical options exist. The more extensive procedure removes the entire affected lung along with surrounding tissue, while the lung-sparing approach removes only the diseased lining and visible tumor while keeping the lung intact. The more radical surgery offers a better chance of removing all visible cancer but carries higher risk of serious complications. The lung-sparing option has fewer post-surgical problems but may leave behind microscopic disease. The choice between them remains one of the most debated questions in mesothelioma treatment.
Chemotherapy
Chemotherapy can be given before surgery to shrink tumors (making them easier to remove), after surgery to target any remaining cancer cells, or as the primary treatment when surgery isn’t an option. A platinum-based drug combined with another chemotherapy agent has been the standard approach for years.
Immunotherapy
In 2020, the FDA approved the first immunotherapy combination for unresectable pleural mesothelioma, meaning tumors that cannot be surgically removed. In the clinical trial that led to this approval, patients receiving immunotherapy lived a median of 18.1 months compared to 14.1 months for those on standard chemotherapy. At the two-year mark, 41% of immunotherapy patients were still alive versus 27% on chemotherapy. Common side effects include fatigue, muscle pain, rash, diarrhea, and nausea. This approval marked a significant shift for patients who previously had limited options beyond chemotherapy.
Multimodal Therapy
The best outcomes generally come from combining two or three of these treatments in sequence. One well-studied approach uses chemotherapy first, followed by surgery, followed by radiation to the surgical site. This “trimodal” strategy has produced median survival times of up to 29 months in select patients. A newer approach reverses the order, delivering radiation in the first week and performing surgery the following week, compressing the entire combined treatment into roughly two weeks.
Who Is Most at Risk
Asbestos exposure remains the dominant risk factor, linked to roughly 80% of cases. The mineral was used extensively in construction, shipbuilding, automotive parts, and industrial insulation throughout the 20th century. Many countries have since banned it, but asbestos still exists in older buildings, and some nations continue to mine and use it.
Men are diagnosed far more often than women, largely reflecting historical patterns of occupational exposure in male-dominated industries. The disease is most commonly diagnosed in people over 65, consistent with its decades-long latency. A small number of cases occur in people with no known asbestos exposure, and radiation exposure and certain genetic factors have been investigated as possible contributors in those cases.