Mesothelioma is a cancer of the mesothelium, the thin layer of tissue that covers most of the body’s internal organs. It most often starts in the lining of the lungs and chest wall, and less often in the lining of the abdomen. According to the National Cancer Institute, exposure to asbestos is the primary cause, and the disease usually appears 20 to 50 years after that exposure.
If someone in your family was just diagnosed, this page and the pages linked from it explain the disease in plain terms, with every medical statement sourced to the National Cancer Institute (NCI), the American Cancer Society (ACS), or the CDC’s Agency for Toxic Substances and Disease Registry (ATSDR). This content is informational only. It is not medical advice, and decisions about testing and treatment belong with your care team.
What causes mesothelioma?
Asbestos. The NCI’s asbestos fact sheet identifies asbestos exposure as the main risk factor for mesothelioma. Asbestos is a group of natural mineral fibers that were used for most of the twentieth century in insulation, shipbuilding, steel production, construction materials, brakes, and hundreds of other products. When those fibers are inhaled or swallowed, some of them stay in the body. Over decades, trapped fibers can cause the cell damage that leads to this cancer.
Most people who develop mesothelioma were exposed at work. Family members could also be exposed at home when workers carried fibers back on their clothing, skin, and hair, a pattern the NCI fact sheet describes as well. If you are trying to work out where an exposure happened, start with our asbestos exposure guide. Pennsylvania’s shipyards, steel mills, refineries, and rail shops used asbestos heavily for decades, which is why this disease still shows up in PA families today.
Why does mesothelioma appear so many years after exposure?
The gap between exposure and diagnosis is called the latency period. Per the NCI, mesothelioma typically develops 20 to 50 years after asbestos exposure. That is why a machinist who left the mill in 1985 can be diagnosed in 2026, and why doctors ask detailed questions about jobs held decades ago. The long delay also matters legally, which we cover at the end of this page.
What are the main types of mesothelioma?
The type is named for where the cancer starts.
- Pleural mesothelioma starts in the pleura, the lining around the lungs. The American Cancer Society reports that roughly 3 out of 4 mesotheliomas are pleural. Read more on our pleural mesothelioma page.
- Peritoneal mesothelioma starts in the peritoneum, the lining of the abdomen, and accounts for most of the remaining cases per the same ACS overview. Read more on our peritoneal mesothelioma page.
- Rare forms can start in the lining around the heart (pericardial) or the testicles. The ACS overview notes these are very uncommon.
How common is mesothelioma, and who gets it?
It is a rare cancer. The American Cancer Society estimates about 3,000 new mesothelioma cases in the United States each year. Because of the long latency period, most people are diagnosed later in life, and men are diagnosed more often than women, which the ACS attributes largely to workplace exposure patterns. A rare cancer has a practical consequence: many local doctors see few or no cases in a career, so families are often referred to larger cancer centers for confirmation and treatment planning.
What are the symptoms, and how is it found?
Early symptoms are easy to mistake for common illnesses. For pleural mesothelioma, the ACS lists shortness of breath, chest pain, cough, and fluid buildup around the lung. Abdominal pain and swelling are more typical of the peritoneal form. Our symptoms page explains why diagnosis so often comes late, and our diagnosis page walks through the imaging and biopsy process step by step.
Once mesothelioma is confirmed, doctors assign a stage that describes how far it has spread, then build a treatment plan around it. These pages cover each part in plain English:
- Mesothelioma stages: what stage 1 through stage 4 actually mean.
- Prognosis and life expectancy: honest, sourced numbers and what they can and cannot tell you.
- Treatment overview: surgery, chemotherapy, radiation, and immunotherapy, as described by NCI and ACS.
What this means for your family
Because asbestos exposure causes almost all mesothelioma, a diagnosis is usually the result of a workplace or product exposure that someone was responsible for. Pennsylvania law generally gives families two years from the diagnosis to file a claim (42 Pa. C.S. § 5524), and separate asbestos bankruptcy trust funds hold roughly $30 billion set aside for people harmed by asbestos, per the U.S. Government Accountability Office (GAO-11-819). You do not need to know which company was responsible before you call. Reconstructing the exposure history is the lawyer’s job, not yours.
Michael C. Schafle, Esq. is a founding partner of Green & Schafle, LLC in Philadelphia and counsel in the Philadelphia asbestos docket (In re: Asbestos Litigation, No. 1986-00001). If mesothelioma has entered your family, request a free case review and get clear answers about your options.