Asbestos is by far the leading cause of mesothelioma, but it is not the only one. Roughly 80% of people diagnosed with pleural mesothelioma (the most common form) report a history of asbestos exposure, which means about 20% do not. That remaining group includes people exposed to other fibrous minerals, people with inherited genetic mutations, those who received radiation therapy for a previous cancer, and a small number of cases with no identifiable cause at all.
Why Asbestos Dominates the Picture
Asbestos fibers are thin, durable, and nearly indestructible once they lodge in tissue. When inhaled, they can work their way into the lining of the lungs (the pleura) or, if swallowed, the lining of the abdomen (the peritoneum). The body cannot break them down, so they sit in place for decades, causing chronic irritation and DNA damage that can eventually trigger cancerous changes. The lag between first exposure and diagnosis is typically 20 to 50 years, which is why cases are still appearing today even in countries that banned asbestos use years ago.
Erionite: A Natural Mineral With Similar Effects
Erionite is a naturally occurring fibrous mineral found in certain rock formations. Its fibers behave much like asbestos: they’re harmless while undisturbed but dangerous when airborne. The clearest evidence of its cancer-causing potential comes from Cappadocia, a region in central Turkey. In the village of Karain, a long-running mortality study found that 53% of all deaths were caused by cancer, and mesothelioma accounted for the vast majority of those cancer deaths. Between 2010 and 2017, 54 out of 66 cancer deaths in the village were mesothelioma. There is no significant asbestos exposure in these communities. The culprit is erionite embedded in the local volcanic rock.
Erionite exposure has also been documented among road construction workers in parts of the western United States, where erionite-containing gravel has been used for road surfacing. The National Cancer Institute recognizes it as a substance associated with increased risks of both lung cancer and mesothelioma.
Inherited BAP1 Gene Mutations
Some families carry mutations in a gene called BAP1 that dramatically raise their risk of several cancers, including mesothelioma. The BAP1 protein normally acts as a brake on cell growth, helping regulate cell division, DNA repair, and cell death. When both copies of the gene are lost or damaged, that brake disappears, and cells become far more likely to grow out of control.
People with BAP1 tumor predisposition syndrome inherit one faulty copy of the gene. If the second copy is damaged later in life (a common event in dividing cells), the result is a complete loss of the protein’s protective function. This genetic vulnerability helps explain why some people develop mesothelioma with minimal or no asbestos exposure. It also helps explain family clusters of the disease. BAP1 mutations don’t guarantee mesothelioma, but they lower the threshold of what it takes for the cancer to develop.
Radiation Therapy as a Risk Factor
People who received radiation to the chest for a previous cancer, such as lymphoma or breast cancer, have roughly twice the risk of developing a second tumor in the irradiated area. Mesothelioma is one of those possible second cancers, though it remains rare. The latency period is long, typically 10 to 30 years between the radiation treatment and a mesothelioma diagnosis. Because the time gap is so large, the connection can be easy to miss.
The SV40 Virus Question
Simian Virus 40 (SV40) has been a subject of debate for decades. The virus contaminated some batches of polio vaccines administered in the late 1950s and early 1960s, potentially exposing millions of people. Lab studies found SV40 sequences in about 60% of mesothelioma tumor samples in one analysis, and the virus was shown to bind to and disable key tumor-suppressing proteins inside cancer cells.
The picture is complicated, though. Researchers in Finland, Austria, and Turkey found no SV40 in their mesothelioma samples, suggesting the virus’s presence in tumors varies by geography. The current thinking is that SV40 is unlikely to cause mesothelioma on its own. Instead, it may act as a co-carcinogen, making cells more vulnerable when combined with asbestos exposure or other damage. Its overall contribution to mesothelioma rates worldwide remains unclear.
Carbon Nanotubes: An Emerging Concern
Carbon nanotubes are manufactured fibers used in electronics, materials science, and other industries. Their shape and durability are strikingly similar to asbestos fibers, which raised early safety concerns. Animal studies have confirmed those worries to a degree. When long carbon nanotubes were introduced into the chest lining of mice, they produced mesothelioma through the same molecular pathway as asbestos, including damage to a key tumor-suppressing gene. Between 10% and 25% of exposed animals developed mesothelioma across multiple experiments.
No human cases of carbon nanotube-induced mesothelioma have been confirmed, partly because widespread occupational exposure is still relatively recent and mesothelioma takes decades to develop. But the animal data is taken seriously enough that occupational health guidelines increasingly call for strict exposure controls in industries that handle these materials.
Mesothelioma in Children and Young Adults
Mesothelioma in children and young adults is exceptionally rare, and its causes look quite different from the adult form. A European study reviewing cases in patients aged 21 and younger, treated between 1987 and 2018, found that only one patient had documented asbestos exposure. The known adult risk factors, including asbestos, BAP1 mutations, and prior radiation therapy, are all uncommon in pediatric patients, and the causes in most young cases remain unexplained.
When No Cause Is Found
Even after careful investigation, some mesothelioma cases have no identifiable exposure to asbestos, erionite, radiation, or any other known risk factor, and no detectable genetic predisposition. These are classified as idiopathic. They represent a real, if small, slice of total diagnoses. The diagnostic process itself does not change based on whether asbestos exposure is present. Diagnosis still requires tissue biopsy, a panel of specialized staining tests to confirm the tumor originates from mesothelial cells, and evidence of tissue invasion seen either under a microscope or on imaging.
For anyone diagnosed without a clear asbestos history, the disease is biologically the same cancer and is treated the same way. The absence of a known trigger does not change the prognosis or the approach to care.