Asbestos has been used in manufacturing since the 20th century. But the relationship between asbestos and cancer arises from the asbestos fiber that has been shown to be extremely hazardous and is now classified as a carcinogen, an agent known to cause cancer. Many of those exposed to it (often at jobsites) have later been diagnosed with cancer.
Mesothelioma, sometimes called "Asbestos Cancer," directly results from inhaling or ingesting asbestos. Though a rare cancer in general, mesothelioma is the most common cancer linked to asbestos. It affects the membranes lining the chest and abdomen and often strikes those who served in the military or worked on jobsites such as navy shipyards.
The fibrous mineral has also been linked with other cancers however. Most notably, asbestos has been tied to lung cancer. This risk may be exacerbated by smoking, if asbestos has a chance to interact with cigarette smoke.
While mesothelioma affects the membranes around the lungs and other organs, lung cancer attacks the tissues of the lungs themselves. Both diseases tend to develop slowly, manifesting many years after the initial exposure, and both are usually fatal.
Some studies have suggested asbestos exposure may increase the risk of various other cancers, including gastrointestinal, colorectal, throat, kidney, esophagus, and gallbladder cancers. Other studies have looked at workers who were exposed to asbestos through inhaling it and found that they experienced increased risk for cancers of the stomach, intestines, esophagus, pancreas, and kidneys. All of these studies are inconclusive however and the precise risk for these cancers has not been determined definitively.
It is unclear what affects, if any, asbestos may have if ingested by swallowing. Some research has found that those who had asbestos in their drinking water did experience higher rates of death from cancer than the average. These people were more likely than most to get cancers of the esophagus, stomach, and intestines. However, it is not clear whether or not asbestos was the cause of this increase.
Though not a cancer, asbestosis has also been linked to asbestos exposure. Asbestosis targets the lungs and describes inflammation there that can lead to symptoms like shortness of breath, coughing, permanent lung damage, and pleural plaques. The pleura, the thin membrane that covers the lungs, can thicken and fluids can gather in the spaces between that membrane and the chest cavity. Those who experience pleural disease due to asbestos exposure may be at increased risk for lung cancer as well.
Asbestos fibers cause cancer and other diseases by entering the lungs, generally via inhalation. The fibers tend to settle on the bottom of the lungs, as revealed in autopsies, and on the diaphragm, a muscle that sits under the lungs and allows them to move. Once in the lungs, asbestos can remain lodged there for years, or even for a person's entire life, though the fibers may be expelled through coughing or swallowed mucus.
In mesothelioma in particular, asbestos fibers lodge in the pleural cavity. Researchers are not sure precisely how asbestos then causes cancer, but two theories currently exist. One posits that asbestos fibers irritate the tissues of the pleura, prompting it to form scar tissue. This immune response leads to inflammation and eventually cancerous, uncontrolled cell reproduction. The other theory suggests that asbestos fibers interfere with the normal functions of mesothelial cells, which line the body's cavities and internal organs. The mesothelial cells, now damaged and unable to regulate their division and growth, build up and lead to cancerous tissue in which cells are multiplying unchecked.