Mesothelioma is not a type of lung cancer. Although the two diseases develop in the same region of the body and share some symptoms, they originate in completely different tissues. Lung cancer begins inside the lung itself, in the cells lining the airways. Mesothelioma starts in the mesothelium, a thin membrane that wraps around the outside of the lungs and lines the chest cavity. This distinction matters because the two cancers behave differently, respond to different treatments, and have different causes.
Where Mesothelioma Actually Starts
Your lungs are surrounded by a two-layered membrane called the pleura. One layer sits directly on the lung surface, and the other lines the inside of the chest wall. The pleura produces a small amount of fluid that lets your lungs slide smoothly as you breathe. Mesothelioma develops in these pleural cells, not in the lung tissue itself. It typically grows as a thickening, sheet-like tumor that encases the lung from the outside rather than forming a distinct mass within it.
On CT scans, this pattern is one of the clearest visual differences between the two cancers. In a study of 50 mesothelioma patients, 92% showed pleural thickening, 86% had thickening along the fissures between lung lobes, and 74% had fluid buildup in the chest cavity. Lung cancer, by contrast, usually appears as a nodule or mass inside the lung.
The pleura isn’t the only place mesothelioma can occur. Similar mesothelial tissue lines the abdomen, the sac around the heart, and the tissue surrounding the testicles. About 10% of mesothelioma cases develop in the abdominal lining (peritoneal mesothelioma), causing swelling, pain, nausea, and weight loss. Pericardial mesothelioma, affecting the heart lining, is rare and can cause chest pain, irregular heartbeats, and fluid buildup. Mesothelioma of the tissue around the testicles is the rarest form of all.
Asbestos, Not Smoking, Is the Primary Cause
The risk profiles for the two cancers are almost opposite. Smoking is the leading cause of lung cancer, responsible for the vast majority of cases. Mesothelioma has no meaningful link to smoking. Its primary cause is asbestos exposure. When asbestos fibers are inhaled, they can lodge in the pleura and cause chronic irritation and genetic damage to mesothelial cells over many years.
The time between first asbestos exposure and a mesothelioma diagnosis is strikingly long. A pooled analysis published in Thorax found a median latency of 38.4 years, and 44% of pleural mesothelioma cases developed more than 40 years after first exposure. The shortest recorded case in the study was about 7.5 years, but that is exceptionally rare. This decades-long delay is one reason mesothelioma is often diagnosed late: the exposure that caused it may have happened in a completely different era of a person’s life.
Three Cell Types of Mesothelioma
Mesothelioma is classified into three cell types, and the distinction has a direct impact on how well treatment works.
- Epithelioid is the most common, making up roughly 69% of cases. These cells grow more slowly and respond best to treatment.
- Sarcomatoid accounts for about 19% of cases. It is more aggressive and often does not respond well to chemotherapy.
- Biphasic is a mix of both cell types and represents about 12% of cases. Its treatment response falls between the other two, depending on which cell type dominates the tumor.
These categories are unique to mesothelioma. Lung cancer has its own classification system, divided primarily into non-small cell and small cell types. The two cancers look different under a microscope, and pathologists use specific protein markers to tell them apart when the diagnosis is uncertain. Mesothelioma cells test positive for certain proteins (calretinin and WT1) that lung cancer cells do not, while lung cancer cells carry a different marker (TTF-1) that mesothelioma lacks. This testing is essential because some cases can look ambiguous on initial biopsy, and the correct diagnosis determines the entire treatment plan.
How Treatment Differs From Lung Cancer
Because mesothelioma grows as a diffuse sheet rather than a contained tumor, surgery looks very different from a typical lung cancer operation. The two main surgical options are removing the pleural lining while preserving the lung, or removing the entire lung along with the surrounding pleura. The lung-sparing approach carries significantly lower risk: a large retrospective review found perioperative mortality of 2.9% compared to 6.8% for whole-lung removal, and complication rates of 28% versus 62%. Median survival was also modestly better with the lung-sparing surgery (16 months versus 12 months). Not all patients are candidates for surgery, and the choice depends on how far the disease has spread.
On the drug treatment side, the FDA approved a new first-line combination for advanced pleural mesothelioma in September 2024. It pairs an immunotherapy drug with standard chemotherapy. In a clinical trial of 440 patients, the combination produced tumor shrinkage in 52% of patients compared to 29% with chemotherapy alone, and median overall survival improved from 16.1 months to 17.3 months. While those numbers may sound modest, they represent meaningful progress for a cancer that has historically had few effective options.
Survival and Prognosis
Mesothelioma carries a more difficult prognosis than many lung cancers. The five-year survival rate for pleural mesothelioma ranges from 7% to 24% depending on the stage at diagnosis. Average survival from diagnosis is about a year and a half for patients who receive treatment. Earlier-stage disease, the epithelioid cell type, and younger age at diagnosis are all associated with better outcomes.
By comparison, lung cancer survival varies enormously by type and stage, but early-stage non-small cell lung cancer has five-year survival rates above 60%. The challenge with mesothelioma is that its long latency period and vague early symptoms (breathlessness, chest wall pain, unexplained fluid around the lungs) mean most cases are caught at an advanced stage. People with a history of asbestos exposure who develop persistent chest or abdominal symptoms should make that exposure history known to their doctor, because it changes which tests get ordered and how quickly.