Asbestos and Cancer

Asbestos related cancer and all other asbestos diseases are caused by tiny fibers that break off from asbestos or products containing asbestos. This process occurs when asbestos products deteriorate and the asbestos becomes “friable,” meaning that it crumbles easily into dust. These microscopic fibers become airborne like fine particles of dust and can be inhaled by anyone in the area without knowing it’s happened or feeling it.

Cancer from Asbestos

Asbestos fibers in the body cause asbestos cancer. For the most part, asbestos cancer develops in the mesothelium, a thin membrane of tissue that protects a number of organs and surfaces within the body. The parts of the mesothelium that cover the chest wall and wrap around the outer surface of the lungs are called the pleura. The peritoneum is the part of the mesothelium covering the abdominal wall. The pericardium wraps around the heart like a sac, providing protection. These are the membranes that make up the mesothelium where mesothelioma develops. The only known cause for mesothelioma is asbestos; specifically, the lodging of asbestos fibers in these membranes that eventually cause the development of malignant cells.

Pleural Mesothelioma Cancer

The most common form of mesothelioma develops in the pleura, the double membrane that lines the lungs and the chest wall. Seventy percent of all malignant mesothelioma cases develop in the pleura, or lung lining. That is why pleural mesothelioma is often called “asbestos lung cancer,” although it is in fact cancer of the outer lining of the lung.

Pleural mesothelioma may develop in a diffuse pattern, with small tumors spread over one of the pleural surfaces. It may develop a single large tumor. In either case it will cause the pleural tissue to thicken and possibly to develop an excess of fluid in the area – a condition known as pleural effusion. Breathing becomes difficult because of the pressure from excess fluid or from the inability of the pleural surfaces to interact smoothly when the lungs are inhaling and exhaling.

Peritoneal Mesothelioma Cancer

This form of asbestos cancer develops in the membrane lining the abdominal cavity. Asbestos fibers that embed themselves in the peritoneum cause malignant cells to develop. As with the pleura, excess fluid may develop causing a distended and painful abdomen. Peritoneal mesothelioma puts pressure on nearby organs and can cause digestive dysfunction. It can also spread malignancy to nearby organs including the liver and the colon, and contribute to kidney problems.

Pericardial Mesothelioma Cancer

This form of asbestos cancer is the rarest; it is found in five percent or less of all mesothelioma diagnoses. Pericardial mesothelioma shares symptoms with the more common pleura mesothelioma: chest pain, a persistent cough and pressure in the chest. When the pericardium thickens with malignant cells or fluid buildup it can put pressure on the heart, causing fibrillation and heart arrhythmia. This variant of mesothelioma may lead to emergency surgery if the pericardium grows to thick and rigid, putting dangerous pressure on the heart.

Asbestos Lung Cancer

Asbestos fibers can cause lung cancer, although usually they are a contributing factor in a cancer patient who is or was a smoker. Since asbestos and cancer have been linked, there have been more diagnoses of asbestos lung cancer with the primary cause being asbestos fibers in the lung tissue. Often the malignancy will come through the lung from the pleura, but more discerning imaging technology and cell diagnosis are now proving that asbestos can also be the cause of malignancy development within the lung as well as without.

Colorectal Cancer

The evidence of a link between colorectal cancer and asbestos is nowhere near as abundant and conclusive as the evidence associating asbestos with mesothelioma cancer. There have been enough associated diagnoses over the years however to generate some research, which has shown some emerging trends that establish a link. One study of 3,897 occupationally exposed men who were involved in a chemotherapy clinical trial for lung cancer. Examination of data showed that heavy smokers with asbestos exposure were at higher risk for colorectal cancer – not a surprise, given the impact of smoking on all types of cancer risk. However the same study showed a strong link between evidence of benign pleural plaques that were the result of asbestos exposure, and ultimate development of colorectal malignancy.4

Gastrointestinal Cancer

There have been several analyses of existing mortality studies that were inconclusive on the question of asbestos exposure and gastrointestinal cancer. One study detected elevated levels of esophageal cancer among factory workers that might be attributed to swallowed asbestos fibers, but the data was inconclusive. A meta-study of death certificate data from 4,943,566 workers that contained information on occupation and industry was conducted in 1997.

The certificates examined were from 28 states, dated from 1979 through 1990. Researchers identified occupations with elevated risk of asbestos exposure based on the occurrences of mesothelioma. They identified twelve occupations with elevated asbestos risk that also exhibited high levels of gastrointestinal cancer. However other high-risk occupations including insulation workers, furnace operators, and plumbers did not show elevated instances of gastrointestinal cancer. Their conclusion was that there is an association between asbestos exposure and gastrointestinal cancer, but the magnitude of the effect is very small.5

Who Is At Risk for Asbestos Cancers?

Millions of people in the U.S. received significant asbestos exposure in the years since the early 1940s, often on their jobs or because their spouses worked in an asbestos-laden environment. Thousands of members of the military, for example, worked with asbestos products as part of the shipbuilding process, or because they built structures that had asbestos-containing materials. Being exposed to asbestos on a daily basis put millions of people at risk for developing asbestos related cancer.

Asbestos cancers are especially common in the following professions, although there are many other lines of work in which asbestos can be present:

  • Submarine personnel
  • Asbestos removal workers
  • Shipyard workers
  • Demolition workers
  • Drywall installers and removers
  • Firefighters
  • Automobile industry workers
  • Automobile mechanics

The History of Asbestos Cancer

Mesothelioma didn’t become a fixture in medical literature until the latter half of the 20th century when the asbestos was finally identified as a dangerous carcinogen. The Federal Government did not start tracking mesothelioma deaths as a specific category until 1999. In that year, the estimated number of deaths from the disease doubled, which suggests that the number of deaths due to mesothelioma prior to 1999 have been severely underestimated.

The National Institute for Occupational Health and Safety reported after five years of tracking that there were 18,068 deaths due to mesothelioma in the United States over that period, with deaths increasing slightly each year.6 There can be no doubt that for the last half of the 20th century the true cause for many deaths reported as due to lung cancer were in fact due to asbestos cancer.

Sources:

  1. National Cancer Institute, http://www.cancer.gov/cancertopics/factsheet/Sites-Types/mesothelioma
  2. Brigham and Women's Hospital, http://www.brighamandwomens.org/mesothelioma/Pleural_Mesothelioma.aspx?subID=submenu2
  3. American Journal of Clinical Pathology, Cagle, January 2002, Medscape, http://www.medscape.com/viewarticle/422880
  4. American Journal of Epidemiology, Oluremi et al, 2005, http://aje.oxfordjournals.org/cgi/content/full/162/9/868
  5. American Journal of Industrial Medicine, Seong-Kyu Kang et al, http://www3.interscience.wiley.com/journal/49390/abstract?CRETRY=1&SRETRY=0
  6. Centers for Disease Contro, 2005, http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5815a3.htm

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