What Is Mesothelioma? Symptoms, Causes, and Diagnosis Explained

What Is Mesothelioma?

Mesothelioma is a rare and aggressive cancer that originates in the mesothelium — a thin layer of tissue that covers most of the body's internal organs. The disease is almost exclusively caused by prior exposure to asbestos, a naturally occurring mineral once widely used in construction, shipbuilding, and manufacturing. According to the American Cancer Society, approximately 3,000 people in the United States are diagnosed with mesothelioma each year.^[1]

Although mesothelioma is not the most common form of cancer, it carries a disproportionately severe prognosis. One of its most defining — and most devastating — characteristics is its extended latency period: symptoms typically do not appear until 20 to 50 years after initial asbestos exposure.^[6] By the time mesothelioma is diagnosed, it has often reached an advanced stage, which limits treatment options and complicates legal claims for workers exposed decades ago.

Because mesothelioma is so directly linked to asbestos exposure, it is recognized as an occupational disease. The National Cancer Institute classifies asbestos as a known human carcinogen, and a diagnosis of mesothelioma with a history of asbestos exposure is generally sufficient to establish the basis for a legal claim.^[7]

Types of Mesothelioma

Mesothelioma is classified by the organ or body cavity where it originates. NIH medical literature identifies four primary types:^[3]

• Pleural mesothelioma (65–70% of cases): Develops in the pleura, the two-layered membrane surrounding the lungs. This is the most common form and is most frequently associated with inhaling asbestos fibers.
• Peritoneal mesothelioma (~30% of cases): Develops in the peritoneum, the lining of the abdominal cavity. It is associated with both inhaling and ingesting asbestos fibers. Patients with peritoneal mesothelioma who are eligible for surgery and HIPEC (heated intraperitoneal chemotherapy) tend to have better outcomes than those with pleural disease.
• Pericardial mesothelioma (<1% of cases): Extremely rare; develops in the lining surrounding the heart (pericardium).
• Testicular mesothelioma (<1% of cases): The rarest form; develops in the tunica vaginalis, a membrane surrounding the testes.

Mayo Clinic further categorizes mesothelioma by cell type — epithelioid (most common, best prognosis), sarcomatoid (most aggressive), and biphasic (mixed). Cell type significantly affects both treatment options and expected survival.^[4]

Signs and Symptoms

Because symptoms of mesothelioma closely resemble those of more common conditions like pneumonia or irritable bowel syndrome, the disease is frequently misdiagnosed in its early stages. The American Cancer Society notes that by the time symptoms become apparent, the cancer has often spread beyond its site of origin.^[5]

Pleural Mesothelioma Symptoms

• Chest pain or pain in the lower back
• Shortness of breath (even at rest in advanced cases)
• Persistent, dry cough
• Pleural effusion (fluid buildup around the lungs causing breathing difficulty)
• Hoarseness or difficulty swallowing
• Unexplained weight loss and fatigue
• Fever and night sweats

Peritoneal Mesothelioma Symptoms

• Abdominal pain or swelling
• Ascites (fluid buildup in the abdomen)
• Nausea, vomiting, or bowel changes
• Loss of appetite and unintended weight loss
• Lumps of tissue under the abdominal skin

Symptoms of pericardial mesothelioma include chest pain and an irregular heartbeat. Any of these symptoms in a person with a history of asbestos exposure — even decades prior — should prompt immediate evaluation by a physician familiar with asbestos-related diseases.

What Causes Mesothelioma? The Asbestos Link

Asbestos is the primary and, in the vast majority of cases, sole cause of mesothelioma. Asbestos consists of naturally occurring silicate minerals that form long, durable fibers resistant to heat and corrosion. These properties made it commercially valuable for most of the 20th century — and catastrophically dangerous to the workers who handled it.

When asbestos-containing materials are disturbed, they can release microscopic fibers into the air. These fibers, when inhaled or ingested, become permanently lodged in the mesothelial tissue lining the lungs, abdomen, or other organs. Over time — typically decades — embedded fibers trigger chronic inflammation, genetic damage, and ultimately malignant cell transformation.^[6]

The NCI notes that asbestos has been classified as a known human carcinogen by the U.S. Department of Health and Human Services, the EPA, and the International Agency for Research on Cancer (IARC). There is no known safe level of asbestos exposure.^[7]

How Is Mesothelioma Diagnosed?

Mesothelioma diagnosis typically involves multiple steps. Because the disease is rare, physicians without experience treating asbestos-related cancers may initially pursue more common diagnoses, which can delay appropriate treatment. The American Cancer Society outlines the standard diagnostic pathway:^[8]

• Medical history review: A thorough occupational and environmental history is essential, including any history of asbestos exposure
• Imaging studies: Chest X-rays, CT scans, MRI, and PET scans can reveal pleural thickening, fluid buildup, or masses suggestive of mesothelioma
• Fluid analysis: Thoracentesis (drawing fluid from around the lungs) or paracentesis (abdominal fluid) may reveal malignant cells, though this alone is rarely definitive
• Biopsy: A tissue biopsy is required to confirm the diagnosis. Methods include needle biopsy, video-assisted thoracoscopic surgery (VATS), laparoscopy, or open surgical biopsy
• Immunohistochemistry: Specialized cell staining distinguishes mesothelioma from lung adenocarcinoma and other cancers that may present similarly

If you have been exposed to asbestos and are experiencing any of the symptoms described above, seeking evaluation at a cancer center with mesothelioma expertise — such as Mayo Clinic's Mesothelioma Specialty Group — can improve diagnostic accuracy and speed access to appropriate treatment.^[4]

Prognosis and Survival Rates

Mesothelioma prognosis depends on several factors, including the type of mesothelioma, cell type, stage at diagnosis, age, and overall health. The American Cancer Society reports overall five-year relative survival rates for pleural mesothelioma (based on SEER data, cases diagnosed 2015–2021) as follows:^[10]

Peritoneal mesothelioma patients who are eligible for cytoreductive surgery combined with HIPEC generally achieve significantly better outcomes, with some studies reporting median survival exceeding 50 months. Research published in PMC identifies epithelioid cell type, younger age, female sex, early stage, and peritoneal location as the strongest positive prognostic factors.^[9]

These statistics represent population averages. Individual outcomes vary substantially, and advances in immunotherapy and surgical technique are improving survival for select patients. Speaking with a mesothelioma specialist can help you understand how these factors apply to a specific diagnosis.

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