Mesothelioma is an aggressive cancer that attacks the mesothelium, which is a thin membrane made of epithelial cells that lines all of the body’s organs as well as body spaces like the thoracic cavity and abdominal cavity. Mesothelioma most often develops in the lining of the lungs and pleural cavity, and is well known for its association with the carcinogen asbestos. In fact, the late Hollywood actor Steve McQueen is known for having developed mesothelioma after years of asbestos exposure while in the military. That said the vast majority of mesothelioma cases stem from asbestos exposure. Asbestos is a mineral that was widely used as construction material in everything from paint to insulation to roofing tiles because it has strong fibers that were resistant to fire and served as good insulation. Asbestos fibers are jagged in shape, and extremely tiny – about 500 times finer than a human hair. If those tiny asbestos fibers get inhaled over time, they make their way into the interstitial space of the lungs and then slowly make their way over to the epithelial cells of the visceral or parietal pleura – both of which are layers of mesothelium.
The microscopic, jagged asbestos fibers are not metabolized or removed from the lungs — so, unlike smoking, whose risk gets lower after you quit, the risk from asbestos exposure stays with you for life. The presence of these fibers leads to an inflammatory response and DNA damage. Eventually, mutations can arise that lead to these epithelial cells dividing uncontrollably, and turning into a tumor. Over time, small cancerous growths called mesothelial plaques start to cover the visceral pleura over the lungs and the parietal pleural under the chest wall. Interestingly, these growths start to express a lot of calretinin, a calcium-binding protein, involved in regulating calcium levels within the cell – and this is something that helps to distinguish mesotheliomas from other types of tumors.
In addition to affecting the lungs and pleural lining, asbestos fibers can also end up in the stomach if saliva containing the material or mucus from the airways is swallowed. Research is also being done to find out whether asbestos fibers are capable of traveling through the lymphatic system. Because asbestos fibers affect epithelial cells, they can cause mesothelioma in nearly any of the body’s internal organs, but it’s most commonly found in the lungs and abdominal organs – the liver, spleen and the bowel – or in very rare cases, the pericardium lining of the heart and testes. Symptoms of mesothelioma affecting the lungs or parietal pleura include chest pain, shortness of breath, pleural effusions, and if the tumor invades into a blood vessel – it can result in bloody sputum.
Occasionally, a mesothelioma can also destroy the lung tissue between the bronchial tree and the pleural space, leading to a pneumothorax – which is air in the pleural space. Diagnosing a mesothelioma typically begins with a chest Xray or CT scan – with key findings being pleural thickening, as well as a pleural effusion or pneumothorax. Ultimately, though, the diagnosis is made with a biopsy of the tumor. In suspected cases of mesothelioma, the tissue sample can be immunostained with an antibody that reacts to the protein calretinin, and it gives the cytoplasm and nuclei of the cancerous cells a distinctive “fried egg” shape. Unfortunately, the prognosis for Mesothelioma is poor unless it’s caught early, this because the cancer is extremely resilient and has typically spread to multiple organs by the time it’s detected.
Treatment depends heavily on the stage of the disease, and usually combines surgery, chemotherapy, and radiation. Alright, as a quick recap – mesothelioma is an asbestos-related cancer that usually involves the lining of the lungs and pleural lining under the chest wall. Tiny asbestos fibers get inhaled, make their way into epithelial cells, and cause DNA damage, which ultimately leads to the formation of mesothelial plaques and pleural thickening..
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