What Is Mesothelioma? A Complete Guide

Definition & Overview

Mesothelioma is a rare, malignant cancer that develops in the mesothelium — the thin layer of tissue that covers most of the body's internal organs. The disease is almost exclusively caused by exposure to asbestos, a naturally occurring mineral that was widely used in construction, shipbuilding, manufacturing, and the military throughout the 20th century.

Approximately 3,000 new cases are diagnosed in the United States each year. Despite being relatively rare, mesothelioma is one of the most serious cancers due to its aggressive nature and the fact that symptoms typically don't appear until decades after initial asbestos exposure — often when the disease has already reached an advanced stage.

Types of Mesothelioma

Mesothelioma is classified by the location in the body where it develops:

• Pleural Mesothelioma — Develops in the lining of the lungs (pleura). This is the most common type, accounting for approximately 80% of all cases.
• Peritoneal Mesothelioma — Develops in the lining of the abdomen (peritoneum). Accounts for about 15–20% of cases and has seen significant treatment advances in recent years.
• Pericardial Mesothelioma — Develops in the lining surrounding the heart. Very rare, accounting for less than 1% of cases.
• Testicular Mesothelioma — Develops in the lining of the testes. Extremely rare, with fewer than 100 cases reported in medical literature.

Learn more about each type of mesothelioma →

What Causes Mesothelioma?

The overwhelming cause of mesothelioma is asbestos exposure. When asbestos fibers are inhaled or ingested, they can become lodged in the mesothelium and cause cellular damage over time, eventually leading to cancer.

High-risk occupations historically associated with asbestos exposure include:

• Construction workers, insulators, and pipefitters
• Shipyard workers and Navy veterans
• Auto mechanics (brake pads and gaskets contained asbestos)
• Firefighters and first responders
• Factory and industrial workers
• Miners and mill workers

"Secondary exposure" is also a significant risk factor. Family members of workers who brought asbestos fibers home on their clothing have developed mesothelioma without any direct occupational exposure.

Read our complete guide to mesothelioma causes and asbestos exposure →

Common Symptoms

Because of the long latency period, mesothelioma symptoms are often mistaken for less serious conditions like pneumonia or irritable bowel syndrome. The most common symptoms of pleural mesothelioma include:

• Persistent dry cough or wheezing
• Shortness of breath (dyspnea)
• Chest pain or tightness
• Pleural effusion (fluid buildup around the lungs)
• Unexplained weight loss and fatigue

Peritoneal mesothelioma symptoms include abdominal pain, swelling, nausea, and changes in bowel habits.

See the full list of mesothelioma symptoms and when to see a doctor →

How Is It Diagnosed?

Diagnosing mesothelioma typically involves a combination of imaging tests (X-rays, CT scans, PET scans), biopsies, and blood tests. Because the disease is rare, it is often misdiagnosed initially. It's important to see a specialist — ideally at a mesothelioma cancer center — for an accurate diagnosis.

Learn about the full diagnostic process →

Treatment Options

Treatment depends on the type and stage of mesothelioma, as well as the patient's overall health. Options include:

• Surgery — Pleurectomy/decortication (P/D) or extrapleural pneumonectomy (EPP) for pleural mesothelioma; cytoreductive surgery with HIPEC for peritoneal mesothelioma
• Chemotherapy — The standard first-line treatment, typically pemetrexed combined with cisplatin or carboplatin
• Immunotherapy — Nivolumab (Opdivo) and ipilimumab (Yervoy) — FDA-approved in 2020 and the current 2025 standard of care — have shown significant survival benefits
• Radiation therapy — Often used in combination with surgery or to manage symptoms
• Clinical trials — New treatments including gene therapy and targeted therapy are being studied

Explore all mesothelioma treatment options in detail →

Prognosis & Life Expectancy

The prognosis for mesothelioma has historically been poor, but outcomes are improving. The average life expectancy after diagnosis is 12 to 21 months, though many patients live significantly longer — especially those diagnosed at an earlier stage and treated at specialized centers.

The 5-year survival rate for all mesothelioma types is approximately 10%, but peritoneal mesothelioma patients treated with surgery and HIPEC have seen 5-year survival rates of 40–50%.

Read our complete guide to mesothelioma prognosis and survival rates →

Legal Rights & Compensation

If you or a loved one has been diagnosed with mesothelioma, you may be entitled to significant financial compensation. Asbestos manufacturers knew about the dangers of their products for decades and concealed this information from workers and the public.

Compensation options include:

• Personal injury lawsuits — Average settlements range from $1 million to $2.4 million
• Wrongful death claims — Filed by surviving family members
• Asbestos trust fund claims — Over $30 billion is available from bankrupt asbestos companies
• VA benefits — For veterans exposed to asbestos during military service

Learn about your legal rights and how to pursue compensation →

The Anatomy of the Mesothelium

To understand mesothelioma, it helps to first understand the mesothelium — the thin layer of tissue that forms the lining of several body cavities. The mesothelium serves multiple functions: it provides a slippery surface that allows organs to move against each other without friction, it secretes fluid that lubricates these movements, and it plays a role in immune surveillance and inflammation. The mesothelium is found in the pleural cavity (surrounding the lungs), the peritoneal cavity (surrounding the abdominal organs), the pericardial cavity (surrounding the heart), and the tunica vaginalis (surrounding the testes).

Mesothelioma can develop in any of these locations, though the pleural cavity is by far the most common site. The disease begins when asbestos fibers — inhaled or ingested — lodge in the mesothelium and cause chronic inflammation and genetic damage over a period of decades. This damage eventually leads to malignant transformation of the mesothelial cells, which begin to divide uncontrollably and form tumors.

How Asbestos Causes Mesothelioma

The relationship between asbestos exposure and mesothelioma is one of the most well-established causal relationships in occupational medicine. When asbestos fibers are inhaled, their needle-like shape allows them to penetrate deep into the lung tissue and reach the pleural lining. Once lodged in the pleura, the fibers cannot be removed by the body's normal clearance mechanisms. Over time, they cause persistent inflammation, generate reactive oxygen species that damage DNA, and directly interfere with cell division — all of which can lead to malignant transformation.

The long latency period of mesothelioma — typically 20 to 50 years between first exposure and diagnosis — reflects the time required for the accumulated genetic damage to reach the threshold for malignant transformation. This latency period is why mesothelioma is still being diagnosed in large numbers today, even though asbestos use has declined significantly since the 1970s. Workers who were heavily exposed to asbestos in the 1950s, 1960s, and 1970s are now reaching the age when mesothelioma typically develops.

Types of Mesothelioma by Location

Pleural mesothelioma, which develops in the lining of the lungs, is the most common type, accounting for approximately 75-80% of all cases. It typically presents with shortness of breath, chest pain, and pleural effusion (fluid buildup around the lung). Peritoneal mesothelioma, which develops in the lining of the abdomen, accounts for approximately 20-25% of cases and presents with abdominal pain, bloating, and ascites (fluid in the abdomen). Pericardial mesothelioma, which develops in the lining of the heart, is extremely rare, accounting for less than 1% of cases. Testicular mesothelioma, which develops in the lining of the testes, is the rarest form, with fewer than 100 cases reported in the medical literature.

Cell Types and Their Significance

Mesothelioma is classified not only by location but also by the type of cells involved. Epithelioid mesothelioma, which accounts for approximately 60% of cases, is characterized by cells that look similar to normal epithelial cells. It is the most responsive to treatment and has the best prognosis of the three cell types. Sarcomatoid mesothelioma, which accounts for approximately 20% of cases, is characterized by spindle-shaped cells that resemble connective tissue cells. It is the most aggressive form and least responsive to treatment. Biphasic mesothelioma, which accounts for approximately 20% of cases, contains both epithelioid and sarcomatoid components and has an intermediate prognosis.

The cell type is determined by pathological examination of biopsy tissue and is an important factor in treatment planning and prognosis. Patients with epithelioid mesothelioma are generally better candidates for aggressive surgical treatment and have longer median survival times than patients with sarcomatoid or biphasic disease. Knowing the cell type is also relevant for legal claims, as it provides important medical context for the damages calculation.

Risk Factors Beyond Asbestos

While asbestos exposure is the primary cause of mesothelioma, accounting for approximately 80% of cases, other risk factors have been identified. Exposure to erionite — a naturally occurring fibrous mineral found in certain volcanic rock formations — has been linked to mesothelioma in communities in Turkey and the United States where erionite is present in the soil. Radiation therapy to the chest or abdomen for other cancers has been associated with a small increased risk of mesothelioma. Simian Virus 40 (SV40), a virus that contaminated some polio vaccines given in the 1950s and 1960s, has been investigated as a possible cofactor in mesothelioma development, though the evidence remains controversial.

Genetic factors may also play a role. Mutations in the BAP1 gene — a tumor suppressor gene — have been found in a subset of mesothelioma patients and their family members, suggesting a hereditary predisposition in some cases. People with BAP1 mutations appear to have a higher risk of developing mesothelioma after asbestos exposure than people without the mutation. Research into the genetic basis of mesothelioma is ongoing and may eventually lead to better risk stratification and targeted treatments.

The Global Burden of Mesothelioma

Mesothelioma is a global disease, with approximately 30,000 new cases diagnosed worldwide each year. The United States accounts for approximately 3,000 cases per year — a number that has remained relatively stable for the past decade, as the decline in new cases from reduced asbestos use has been offset by the aging of the population exposed decades ago. Other countries with high mesothelioma rates include the United Kingdom, Australia, and several European countries that had significant asbestos industries.

In many developing countries, mesothelioma rates are expected to increase in the coming decades as asbestos use — which continues in many parts of the world — leads to future diagnoses. The World Health Organization estimates that approximately 125 million people worldwide are currently exposed to asbestos in the workplace, and that asbestos causes approximately 107,000 deaths per year from mesothelioma and other asbestos-related diseases. Despite this toll, asbestos is still not banned in many countries, including the United States, where it continues to be used in limited applications.

Frequently Asked Questions