Asbestos Lung Cancer
Asbestos lung cancer is a rare type of lung cancer, which is the most common cause of cancer death in the United States. An estimated 4,800 deaths a year are linked to this illness, a number that represents about 4 percent of all U.S. fatalities connected to cancer of the lungs. The overwhelming majority of other deaths — about 90 percent — are linked to smoking.
Medical researchers first made a probable causal relationship between exposure to asbestos and lung cancer in 1935. Seven years later, a member of the National Cancer Institute confirmed asbestos as a cause of lung cancer. Study after study continued to show the cause-effect relationship of asbestos and lung cancer. The Occupational Safety and Health Administration (OSHA) in 1986 proclaimed lung cancer as the greatest risk for Americans who worked with asbestos.
Like mesothelioma, another asbestos-related cancer, lung cancer associated with asbestos is typically diagnosed at a late stage of development because of the long latency period of development and the onset of symptoms.
Similarities and Differences of Mesothelioma and Asbestos Lung Cancer: Both take decades to develop, but only months to spread to distant organs. They have similar diagnostic procedures and treatment techniques; however, the diseases differ in physical characteristics and non-asbestos risk factors. .
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How Asbestos Causes Lung Cancer
Companies and manufacturers have mined and used asbestos, a naturally occurring mineral, for commercial purposes in North America since the late 1800s. It is now highly regulated and a number of countries, including U.S. government agencies, classify it as a human carcinogen. When someone disturbs an asbestos-containing product, they release the microscopic fibers into the air. If inhaled, these thin fibers can become trapped in the lungs. Over long periods of time, they can accumulate and cause inflammation, scarring and other critical health problems. In some cases, the fibers can even trigger the development of lung cancer.
Researchers report the duration and concentration of asbestos exposure plays a role in the risk of developing lung cancer. The Helsinki Criteria states the risk for lung cancer increases as much as 4 percent with each year of exposure. OSHA has demonstrated a clear association between the concentration of asbestos exposure and the risk of lung cancer, finding the higher the concentration of asbestos fibers, the higher the risk of lung cancer.
The implications of asbestos exposure are not apparent immediately following exposure. When asbestos fibers are first inhaled, they can become lodged in the lining of the lungs. The size of asbestos fibers affects where they become lodged, having implications on whether lung cancer or mesothelioma develops. Researchers discovered that 3mm fibers are more likely to become lodged in the lining of the lungs, whereas 5mm fibers (1/5 inch) tend to lodge in the lung tissue and increase the risk of developing lung cancer.
After many years, sometimes decades, these fibers cause enough irritation and cellular damage to generate tumor formation. Whether someone develops lung cancer, mesothelioma or asbestosis will depend on a person's health, genetics, habits and the duration and concentration of exposure.
Workers in certain trades and professions, most of them industrial, carry elevated risks of developing asbestos-related lung cancer. Shipyards, which have notoriously poor safety records, exposed workers to widespread asbestos until the mid-1970s. Many employees rarely wore necessary protective gear, and nearly all shipyard workers placed themselves at risk for lung cancer, asbestosis and mesothelioma.
But shipyards workers are hardy the only trade considered high risk for this type of lung cancer. Any occupation in which people are in a confined area where asbestos is present — or where asbestos dust is circulated — is dangerous.
Veterans are a high-risk group for developing lung cancer related to asbestos for several reasons. The U.S. military exposed its service members to asbestos for decades because ships, submarines, tanks, planes and barracks were built with asbestos parts and products. Second, upon completing their military service, many veterans immediately were qualified to for civilian work in trades that also were rife with exposure.
New York Connection
About 13,500 cases of the disease are diagnosed yearly in New York, thanks in large part to the many asbestos-laden job sites and the state's history of lowered safety regulations.
As is true for many people who develop the disease, the majority of these patients in New York developed the disease after exposure at work. New York's history with the shipbuilding industry, shipyards, foundries and other blue-collar occupations contribute to the overall high asbestos cancer rates in the state.
Latency Period of the Disease
All asbestos-related diseases have a long latency period from the time of initial asbestos exposure to the development of an illness. Asbestos-related lung cancer is no different, typically taking between 15 and 35 years to develop. Studies show latency is affected by the level of exposure and co-carcinogens such as cigarettes.
Lung cancer development begins long after asbestos fibers have reached the lungs. Once asbestos fibers are inhaled, they attach to the lung tissue because of their jagged-like structure. When the fibers cause enough irritation, inflammation and genetic damage, tumor formation begins.
For doctors to attribute lung cancer to asbestos exposure, many say at least 10 years must pass from the time of exposure to cancer development. Multiple studies suggest the cancer is most likely to develop between 30 and 35 years after exposure, with the onset of cancer decreasing near the 40-year mark.
The Helsinki Criteria were established in 1997 to help doctors determine if lung cancer and other pleural diseases are asbestos-related. If a person's lung cancer is diagnosed as asbestos-related, it must fit two criteria:
The first addresses the latency period:
- Lung cancer must develop at least 10 years after initial exposure to asbestos.
Asbestos-related lung cancer has a minimum latency period of 10 years. If a person is diagnosed within a decade of his or her first exposure to asbestos, the exposure is ruled out as a possible contributing factor. If a patient developed lung cancer 10 or more years after initial exposure, they fit the first criterion. To prove that asbestos contributed to the development of lung cancer, the patient must fit only one of the remaining Helsinki Criteria:
- Diagnosis of asbestosis.
- Higher than normal asbestos fibers in the lung tissue. The number of asbestos fibers is measured per gram of dry lung tissue and must coincide with the amount seen in asbestosis patients. The exact amount varies based on type and length of asbestos fibers.
- Higher than normal exposure to asbestos, measured in fibers per milliliter of air a year (fibers/mL-yr). The patient must have been exposed to levels of airborne asbestos equal to 25 f/mL-yr. To reach this threshold in a one-year work period, the patient must have been exposed to a level of 25 f/mL. Such a high level is typically only found in asbestos manufacturing and asbestos insulation work. To reach 25 f/mL-yr in a five-year period, an individual must have been exposed to asbestos at a level of 5 f/mL. This level is typical of shipbuilding and construction work.
In 2004, researchers reviewed new study results that had emerged since the Helsinki Criteria first were formed. Researchers concluded the 17-year-old criteria still held. But they amended the list to answer a common question.
Researchers more closely considered the role of smoking in asbestos-related lung cancer, stating that a second cause of cancer complicates the issue. Most lung cancer cases are linked to smoking, and some are further linked to asbestos. The authors are careful to note the secondary attribution is difficult to determine. Because asbestos and smoking work together synergistically, researchers suggest it is especially difficult to distinguish smoking-related cases from those caused by both smoking and asbestos.
The Helsinki Criteria at work: Suppose a man is diagnosed with lung cancer and worked as a shipbuilder 30 years earlier for several years. The individual fits the first criterion: his first exposure to asbestos was more than 10 years before his diagnosis. He also fits one of the remaining criteria: his occupation exposed him to asbestos at a level of at least 25 f/mL-yr. Because of these two risk factors, doctors would conclude that asbestos caused or contributed to the man's lung cancer.
Criticism of the Helsinki Criteria
The main critique of the Helsinki Criteria is a result of contradictory hypotheses relating asbestos exposure to lung cancer.
There are three distinct and conflicting hypotheses about asbestos exposure causing lung cancer:
- Asbestos exposure only increases the risk of lung cancer when it has caused asbestosis.
- Asbestos exposure increases the risk of lung cancer when it is enough to cause asbestosis, despite whether it actually led to an asbestosis diagnosis. This is the hypothesis favored by the Helsinki Criteria.
- Asbestos exposure always increases the risk of lung cancer, absent of any threshold needed for asbestosis.
The Helsinki Criteria specifically state that asbestosis is not necessary to prove a causal relationship, but that asbestosis must have been possible based on the amount of exposure. Researchers who disagree with this hypothesis disagree with the Helsinki Criteria. Proponents of the first hypothesis argue the criteria are too lenient, and supporters of the third hypothesis argue they are too strict. Despite some opposition, the Helsinki Criteria are an accepted standard throughout the world.
Other Sets of Criteria to Determine Asbestos Association
Countries struggling with asbestos-related health problems lay out their own versions of the Helsinki Criteria. Panels of experts worldwide typically accept the Helsinki Criteria as a valid set of guidelines and make minor changes specific to each country. The American Thoracic Society (ATS) lays out criteria to determine if a disease is caused by asbestos. The ATS states that, although its guidelines are outlined for nonmalignant diseases and not lung cancer, they coincide with the Helsinki Criteria.
The AWARD (Adelaide Workshop on Asbestos-Related Diseases) Criteria, another set of widely recognized standards, was laid out in 2000 to determine the utility of the Helsinki Criteria in Australia. In making the AWARD Criteria, Australia's experts made minor alterations to reflect the specific types of asbestos found in the country. Overall, the panel of experts deemed the Helsinki Criteria to be reasonable and applicable.
Asbestos-Related Lung Cancer and Asbestosis: After much debate, the medical community now believes the presence of asbestosis is a reliable diagnostic marker that a patient has received enough asbestos exposure to develop lung cancer. Some studies claimed asbestosis must be present for lung cancer to be associated with asbestos, while others stated the two can exist independently. Asbestosis and lung cancer are commonly associated because the risk for both rises in a parallel manner as asbestos fibers accumulate in lung tissue. Evidence shows the level of exposure required to develop asbestosis and lung cancer is similar.
Asbestos-Related Lung Cancer and Smoking
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The risk for lung cancer is much higher among asbestos-exposed smokers because the combination of asbestos and smoking greatly impairs lung function. When someone smokes, the efficiency of cilia (responsible for cleaning the lungs) is reduced and the lungs' ability to dispel asbestos fibers is significantly weakened. Researchers propose that cigarette smoke fosters the accumulation of asbestos fibers, and with more fibers retained in the lungs the risk for lung cancer increases.
The combination of the effects from asbestos exposure and smoking is referred to as a multiplicative effect. According to the Agency for Toxic Substances and Disease Registry, a cigarette smoker exposed to asbestos is 50 to 84 times more likely to develop lung cancer.
Asbestos-exposed smokers can lower their risk for lung cancer by quitting the habit, but unfortunately the effects of asbestos exposure are irreversible. Those who have smoked and been exposed to asbestos are advised to stop smoking immediately and receive annual screenings for lung cancer.
Prognosis and Survival Rates
The prognosis and survival rate for someone with lung cancer related to asbestos differs by type and subtype of the disease and also by the stage at which the cancer is found. Overall, the median survival for a limited stage small cell patient, with combination chemotherapy, is 16 to 22 months. For patients with extensive stage cancer, the median survival is nine to 11 months with the same treatment.
A 2008 review of medical literature found that adenocarcinoma is almost always associated with longer survival times. A 2011 study agreed with these findings, reporting that adenocarcinoma patients lived a median of 8.4 months while all other NSCLC patients lived a median of 8.1 months. While the difference is small, researchers believe it to be significant.
Types of Lung Cancer
There are two primary forms of asbestos lung cancer: small cell lung cancer and non-small cell lung cancer. Non-small cell lung cancer is less aggressive and more common, accounting for at least 80 percent of all lung cancer cases. Small cell lung cancer makes up less than 20 percent of cases and is more difficult to treat.
About 6 percent of small cell lung cancer patients live five years or longer, but early treatment can improve survival rates significantly. About 17 percent of non-small cell lung cancer patients live five years or longer, nearly three times the percentage for small cell lung cancer.
Small Cell Lung Cancer
- Less than 20% of lung cancer cases
- More Aggressive
- Fewer Treatment Options
- Shorter Life Expectancy
6% Live 5 Years or Longer
Typically originating in the bronchi near the center of the chest, SCLC is aggressive and spreads quickly throughout the body. In many cases the cancer can disperse from its initial location before presenting any symptoms. If symptoms do arise, they are usually nonspecific and can include an atypical cough, chest pain and weight loss.
There are three varieties of small cell lung cancer:
- Small cell carcinoma (oat cell cancer)
- Mixed small cell / large cell carcinoma
- Combined small cell carcinoma
The majority of small cell lung cancer cases are oat cell type. Although the cancer cells are smaller in size compared to non-small cell lung cancers (NSCLC), which make up 85 to 90 percent of all lung cancers, SCLC grows quickly and produces large tumors.
In the early stages of development these tumors can rapidly spread to other parts of the body such as the lymph nodes, bones, liver, adrenal glands and the brain. Unfortunately, surgery is rarely an option with SCLC because of this factor. Doctors instead rely upon chemotherapy that attacks cancerous cells all throughout the body.
Non-Small Cell Lung Cancer
- 80% of lung cancer cases
- Less Aggressive
- More treatment options
- Better prognosis
17% Live 5 Years or Longer
There are three primary subtypes of NSCLC distinguishable by the appearance and chemical makeup of their cells:
- Squamous cell (epidermoid) carcinoma - The most common variety of NSCLC, these cancers form in flat cells that line the inside airways of the lungs. About 25 to 30 percent of all lung cancers are squamous, and this is the most prevalent type of NSCLC among men.
- Adenocarcinoma - Forms in mucus-producing glandular tissues that line the outer parts of the lungs. It is more common in women than men and the predominant type of cancer among non-smokers.
- Large cell (undifferentiated) carcinoma - Appearing in any part of the lung, this type of cancer grows and spreads more rapidly than the other varieties of NSCLC. Accounting for 10 to 15 percent of lung cancers, large cell carcinoma appears to be decreasing in occurrence due to advances in diagnostic techniques.