Lung cancer is the second-most common cancer in both men and women in the US, and by far the leading cause of cancer death in the US, accounting for about 20% of all cancer deaths–this is more than the total for colon, breast, and prostate cancer deaths combined. Lung cancer is very rare before the age of 45; the average age of diagnosis is around 70.
The lungs are two sponge-like organs divided into lobes; the right lung has three lobes, and the left lung has two (the heart takes up more room in that side of the chest cavity). Air enters the lungs via the trachea (windpipe) which splits into bronchi that enter each lung. Tiny air sacs within the lungs known as alveoli absorb oxygen into the blood and expel carbon dioxide. This oxygen / carbon dioxide exchange is the main role of the lungs in the body.
Lung cancer can cause a range of symptoms, including:
A lingering cough
Coughing up blood or rust-colored phlegm/spit
Unexplained weight loss and/or loss of appetite
Hoarseness
Wheezing
Chest pain that increases when breathing deeply, coughing, or laughing
Shortness of breath
Fatigue
Recurrent or chronic bronchitis and/or pneumonia infections
These symptoms may have other causes, and should be evaluated by a medical professional.
Some forms of lung cancer can cause syndromes, or clusters of symptoms, that might not be immediately identifiable as lung-related.
Horner syndrome affects nerves that lead to the eye and face, and can be caused by tumors in the upper lungs. This may cause:
Drooping/weakness in one eyelid
A smaller pupil in one eye
Little or no sweating on one side of the face
Sometimes, lung cancers can cause paraneoplastic syndromes, which affect distant organs or tissues, even though the cancer has not spread there. These syndromes can cause a range of additional symptoms, including nausea, vomiting, water retention, dizziness, loss of balance, changes in vision, difficulty speaking or swallowing, memory loss, mood changes, and difficulty sleeping. Most of these symptoms are unlikely to indicate lung cancer, but if you are experiencing any of these symptoms and can’t determine another explanation, paraneoplastic syndrome is a possibility to raise with your doctor.
Different forms of lung cancer are characterized by distinct features and biological behaviors:
Non-small cell lung cancer (NSCLC): A significant majority of lung cancers–80-85%--are NSCLCs. The treatment and prognosis for NCSLCs is generally similar, but some changes are determined by subtype: some text
Adenocarcinoma: The most common variety of NSCLC, adenocarcinomas form in the epithelial cells, which line the surface of the lungs. Though more common in smokers and former smokers, this form of lung cancer is the most common form in non-smokers. It is more common in women, and in younger patients it is the most common diagnosis.
Squamous cell carcinoma: The squamous cells are flat cells lining the interiors of the airways in the lungs. Cancers that start in these cells are usually found near a main airway, and are often linked to smoking.
Large cell / undifferentiated carcinoma: This form of cancer can begin in any part of the lung, and tends to grow and spread more quickly than other types of NSCLC.
Small cell lung cancer (SCLC): About 10-15% of lung cancers are SCLCs. These cancers tend to spread more quickly, and have usually spread outside the lungs at the time of diagnosis. Even when treatment is successful, SCLCs tend to return.
Other lung cancers: There are many additional subtypes of lung cancer: lung carcinoid tumors, adenosquamous carcinoma, adenoid cystic carcinoma, sarcomatoid carcinoma, and lung lymphomas and sarcomas are all very rare forms of lung cancer.
There are also benign tumors that can form in the lungs. These may or may not require treatment.
Lung cancer survival rates are based on how far the cancer has spread:
Localized: There is no sign the cancer has spread outside the lungs.
Regional: The cancer has spread to nearby structures or lymph nodes
Distant: The cancer has spread to distant parts of the body, such as the liver or bones.
Outcomes vary widely based on the type of lung cancer.The 5-year survival rate for NCSLCs vs. SCLCs is shown below:
Incidence
Below is the overall incidence of lung cancer by age group:
Risk Factors
There are several confirmed risk factors that contribute to an individual’s risk for lung cancer:
Smoking & secondhand smoke exposure: Smoking and secondhand smoke is believed to cause about 80% of all lung cancer deaths, and that number might be higher for SCLCs. Tobacco smoke contains numerous carcinogens that can lead to genetic mutations and uncontrolled cell growth, ultimately resulting in cancer, and these risks increase the longer you smoke.
Radon exposure: Radon is an odorless, colorless, radioactive gas that forms naturally from the breakdown of uranium in soil, rocks, and water. It can become trapped in indoor spaces, leading to dangerous concentrations that can damage lung tissue and eventually lead to cancer. Radon is second only to smoking as a cause of lung cancer. If you have tested for radon in your home and determine levels are too high, there are various forms of radon remediation that can help reduce the risk it poses.
Asbestos exposure / other workplace exposures: Working with asbestos–in textile mills, mines, or shipyards, among other trades–significantly increases lung cancer risk. Significant exposure can lead to a specific form of cancer, malignant mesothelioma. Exposure to diesel exhaust, radioactive elements, or inhaled chemicals (such as silica, nickel compounds, arsenic, beryllium, chromium compounds, or mustard gas, among others) also increases risk.
Beta-carotene supplementation: Particularly in smokers, beta-carotene supplementation has been shown to increase one’s risk for lung cancer. Until more is understood about the mechanisms behind this increase, beta-carotene supplementation should be avoided, regardless of smoking status.
Arsenic in drinking water: Studies have shown a strong correlation between arsenic in drinking water and lung cancer. In the United States, individuals who drink well water are most likely to experience this form of exposure.
Air Pollution: The particulate matter in air pollution can build up in the lungs, damaging the cells over time and eventually leading to cancer.
Health conditions: some text
Chronic bronchitis / recurrent pneumonia: These diseases of the lungs can damage the lung tissue, and when chronic or frequent, they raise the risk of developing lung cancer.
Emphysema: This disease results from damage to the walls of the alveoli (air sacs) within the lungs, and causes shortness of breath. It doubles the risk of lung cancer.
Chronic obstructive pulmonary disease (COPD): This condition is caused by damage to the airways, usually as the result of smoking or exposure to air pollution. It can cause coughing, wheezing, shortness of breath, and fatigue, and like emphysema, it doubles one’s risk of lung cancer.
Alpha-antitrypsin deficiency (AAT): This rare genetic disorder affects the lungs and liver, and can cause emphysema in affected individuals.
Family History: Siblings and children of individuals diagnosed with lung cancer are at higher risk of developing the disease, particularly if the relative was diagnosed at a young age. Whether this is due to genetic predisposition or shared environmental causes is unknown.
Marijuana smoking / e-cigarette use: Though links between lung cancer and marijuana smoking and/or e-cigarette use have not definitively been shown, there is reason to believe they may increase risk. Marijuana smoke contains many of the same toxic substances as cigarettes, and the FDA has determined that e-cigarettes can cause lung damage. The recent introduction of e-cigarettes, and the recent legalization of marijuana, mean that more studies are needed into their impact on diseases such as lung cancer.
Protective Factors
Several factors have been shown to have protective effects against lung cancer:
Quit smoking: Smoking definitively causes lung cancer, and that risk increases the more you smoke and the longer you smoke. However, the body begins to repair itself almost immediately after quitting. Even individuals who have smoked for many years can benefit from quitting, as the risk decreases with each year of abstinence. Quitting smoking at any age can significantly reduce the risk of cancer and other smoking-related diseases, many of which are themselves risk factors for cancer.
Physical activity: Regular exercise can reduce your risk of several types of cancer through a combination of physiological, hormonal, and immunological changes, and has been shown to reduce the risk of lung cancers. It can reduce inflammation, improve immune function, improve hormonal regulation, and lower insulin levels. The American Cancer Society recommends engaging in at least 150 minutes of moderate activity or 75 minutes of vigorous activity each week. Furthermore, data indicates that individuals can see significant incremental benefit with additional exercise.
Fruit / vegetable consumption: Fruits and vegetables are rich in various nutrients which have been shown to have protective effects against multiple cancers, including lung. These foods contain a variety of antioxidants, which help neutralize free radicals in the body and reduce inflammation.
Limit alcohol consumption: Individuals who drink alcohol, particularly those who drink heavily, have a higher risk of lung cancer. Limiting your alcohol intake can reduce your risk. Men should aim to consume less than 2 drinks per day, and women should target 1 or fewer.
Limit red and processed meat consumption: Multiple studies have shown an increase in lung cancer correlating with red meat and processed meat consumption. The increase in risk appears to be dose responsive, meaning that the more red or processed meat one eats, the higher the overall risk.
Screening
Early detection of lung cancer has a dramatic impact on prognosis. The 5-year survival rate for localized NSCLC is around 63.7%, but drops to just 8.9% once the cancer has spread to distant parts of the body. For SCLCs, distant cancers have a 5-year survival rate of just 3%.
More screening
Depending on your age and risk factors, the optimal lung cancer screening will vary:
Regular physicals / medical history: Because lung cancer symptoms may look like something else, it’s important to regularly visit your doctor and mention any new or worsening symptoms at every appointment. They can help you determine when further testing might be warranted.
Low dose CT scans (LDCT): While routine chest x-rays have not led to improved outcomes from lung cancer, regular LDCT screening has proven effective in catching cancers earlier, leading to better survival rates. For high-risk individuals, such as longtime smokers, annual LDCT screening is recommended.
Other imaging tests: Chest x-rays, MRIs and PET scans can also help doctors diagnose lung cancer, or determine how far it has spread. In the absence of other risk factors or symptoms, these tests aren’t routinely recommended.
Sputum cytology: In this test, a sample of sputum (coughed-up mucus) is analyzed for the presence of cancer cells. This form of testing won’t catch all types of lung cancer, and a negative result may lead to further testing if lung cancer is suspected.
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