Lung cancer results from an abnormality or uncontrollable growth in the cells of the lung. The cancer can either begin in the cells of the lung or occur when a tumor that starts in another part of the body spreads into the lung. While lung cancers can start in any part of the lung, more than 90 percent arise in the cells lining the bronchi and bronchioles (larger and smaller airways). In rare cases, lung cancers may start in the pleura or in the supporting tissues of the lungs, such as blood vessels.
How common is lung cancer?
Cancer of the lung is the leading cause of cancer-related deaths in men and women across the globe. In the United States, more than 220,000 new cases and more than 158,000 deaths occur each year due to lung cancer. About 6.5 percent of men and women in the U.S. will have lung cancer in their lifetime. However, lung cancer is mainly a disease of the elderly with up to 70 percent of people diagnosed with the cancer being over 65 years old, while only about 3 percent of the cases occur in people younger than 45.
Risk factors and causes of lung cancer
Lung cancer is closely related to cigarette smoking, with almost 90 percent of cases directly linked to tobacco smoking. Tobacco smoke contains more than 4,000 chemical compounds that have been shown to be carcinogenic (cancer-causing), with the primary carcinogens being polycyclic aromatic hydrocarbons and nitrosamines. The risk of lung cancer grows with the number of cigarettes smoked and the length of time smoking has occurred. For example, among individuals who smoke two or more cigarette packs per day, 1 in 7 will die of lung cancer. Cigar and pipe smoking also can cause lung cancer, but the risk is lower than that of cigarette smoking.
2. Passive smoking
When non-smokers who work or live with tobacco smokers inhale the smoke this is called passive smoking. Studies have shown that non-smokers living with smokers have a 24-percent higher risk of developing lung cancer than non-smokers who do not live with smokers. The risk increases with the number of years of exposure and the number of cigarettes used by the smoker. Every year, more than 7,000 lung cancer deaths in the U.S. are a result of passive smoking.
3. Exposure to asbestos fibers
Asbestos fibers produce silicate fibers that remain in the lungs for several years after exposure. The fibers irritate and damage lung tissue and cause both lung cancer and mesothelioma (cancer of both abdominal lining and pleura of the lung). The risk of asbestos related cancer increases greatly among cigarette smokers. In the past, asbestos related cancer was common because of the extensive use of asbestos in acoustic and thermal insulation. Today, asbestos use is banned in the U.S. and the cases of asbestos related lung cancer have been reduced
4. Lung diseases
Certain lung diseases, such as pulmonary fibrosis (scarring of the lung) and chronic obstructive pulmonary disease (COPD), increase the risk of lung cancer. The risk is even greater if lung diseases occur in cigarette smokers.
5. Familial predisposition
Lung cancer occurrence is more likely in smoking and non-smoking persons whose relatives have had lung cancer. In fact, it is believed that people can inherit certain genes that predispose them to lung cancer.
6. Exposure to radon gas
About 12 percent (21,000) of lung cancer deaths annually in the U.S. are due to radon gas, a natural radioactive gas emitted when uranium decays. Radon gas travels through soil and enters homes through gaps in the drains, foundation, pipes or other openings, with more than 1 in every 15 homes in the U.S. containing dangerous levels of the gas. The risk of lung cancer increases drastically if cigarette smokers are exposed to radon gas.
7. Air pollution
Pollution of the air by power plants, industries and vehicles increases the risk of lung cancer. About 1-2 percent of lung cancer deaths in the United States are associated with breathing polluted air.
8. Previous history of lung cancer
If you are a survivor of lung cancer, you have a higher risk of developing a second lung cancer than a member of the general population has to develop a first lung cancer. Survivors of small-cell lung cancers (SCLCs) have greater risk than survivors of non-small cell lung cancers (NSCLCs).
9. Exposure to diesel exhaust
Exhaust released from diesel engines contains gases and particulate matter (soot). For people frequently exposed to exhaust, such as toll booth workers, truck drivers, forklift, dock and railroad workers, miners, mechanics and garage workers, the risk of getting lung cancer is small but significant.
Types of lung cancer
Cancers arising in the lungs are broadly categorized as small cell lung cancers (SCLCs) and non-small cell cancers (NSCLCs) depending on how cells of the tumors appear on the microscope. Small cell lung cancers (SCLCs) are aggressive, rapidly spreading cancers strongly linked to cigarette smoking. They comprise just about 20 percent of lung cancers, but can spread extensively to other parts of the body. Non-small cell lung cancers (NSCLCs) account for around 80 percent of lung cancers.
Small-cell lung cancers (SCLCs) include:
- Bronchial carcinoids: Rare cancers found in people younger than 40. They grow and spread slowly and account for 5 percent of lung cancers.
- Cancer of tissues supporting the lungs such as blood vessels, smooth muscle and cells of immune system.
Non-small cell lung cancers (NSCLCs) include:
- Adenocarcinomas: Lung cancer arising in the outer (peripheral) areas of the lungs. They are associated with smoking and make up 50 percent of all NSCLCs.
- Bronchioloalveolar carcinoma: Cancer arising at different areas of the lungs and spreading along alveolar walls.
- Squamous cell carcinomas: Lung cancer arising in the central chest area, specifically in the bronchi. Makes up 30 percent of all NSCLCs.
- Large cell carcinomas: A very rare form of NSCLC.
- Mixtures: When different types of NSCLCs occur together.
Signs and symptoms of lung cancer
Lung cancer symptoms usually vary depending on the type, location and extent of spread of the cancer. In fact, lung cancer will not cause pain or obvious symptoms in some people, but will cause pain and severe symptoms in others.
People with lung cancer may have:
- No symptoms: About 25 percent of people with small, single masses of lung cancer will show no symptoms and the cancer can only be detected through a CT scan or chest X-ray.
- Symptoms associated with lung cancer: When lung cancer grows and invades tissues, it may cause different problems such as shortness of breath, coughing, chest pain, wheezing, and coughing blood. Invasion of nerves may result in shoulder pain or hoarseness of voice if vocal cords are paralyzed. Obstruction of a large airway may cause abscesses and pneumonia, while invasion of the esophagus may cause difficulty in swallowing.
- Symptoms associated with spread of lung cancer: Spread of lung cancer to bones may cause pain while spread to the brain may lead to headaches, seizures, blurred vision, loss of sensation and weakness.
- Nonspecific symptoms: While not specific, symptoms such as fatigue, weakness, weight loss, depression and mood changes may be found in people with lung cancer.
You should see a doctor if you have:
- Blood in sputum.
- Chest pain.
- Worsening of an existing cough or if a new cough is persistent.
- Unexplained fatigue or weight loss.
- Persistent bronchitis.
- Repeated respiratory infections.
- Breathing difficulties, such as wheezing or shortness of breath.
Diagnosis of lung cancer
Doctors use a broad range of procedures to diagnose lung cancer. These include:
- Physical examination and medical history: Doctors ask questions to find out risk factors and symptoms of lung cancer. Physical examination helps to investigate lung function and detect chronic lung disease.
- Imaging tests: A chest X-ray is the most common imaging procedure for lung cancer. Other procedures include CT scan, spiral CT scan, MRI scan and PET scan.
- Sputum cytology: For patients who are coughing and producing sputum, the sputum can be examined under microscope for presence of cancerous cells.
- Biopsy: A tissue sample can be obtained from the lung and examined under a microscope for cancer cells. Various techniques used to obtain the tissue sample include fine needle aspiration (FNA), bronchoscopy, thoracentesis, or a major surgical procedure. A tissue sample also may be obtained from lymph nodes and other areas to find out if the cancer has spread.
- Blood tests: Routine blood tests such as for enzymes alkaline phosphatase, aspartate aminotransferase and alanine aminotransferase may help to determine the extent of spread of lung cancer to the liver, bones and other areas.
- Bone scans: Used to determine whether lung cancer has spread to the bones.
- Molecular testing: For advanced lung cancer, tests can be run to check genetic mutations in the tumor cells.
Staging of lung cancer
Lung cancer stage is the measure of how much the cancer has spread in the body. During staging, cancer size, penetration of surrounding tissues and spread to lymph nodes and other organs is evaluated. Several tests are used, including X-rays, blood chemistry tests, bone scans, CT scans, MRI scans and PET scans. The goal is to gather sufficient information for use in selecting and planning for appropriate treatment.
NSCLC stages include:
- Stage I: Lung cancer still only in the lungs and has not spread to lymph nodes. Tumor is still small, around 2 inches (5-centimeters) across.
- Stage II: Tumor is bigger than 2 inches across and has spread to nearby structures such as pleura, chest wall, diaphragm or lymph nodes.
- Stage III: Tumor is quite large and has invaded other organs, with lymph nodes far away from the lung being involved.
- Stage IV: The cancer has extensively spread beyond the chest.
SCLC stages are two:
- Limited stage (LS): Cancer still confined to its area of origin in the chest.
- Extensive stage (ES): Cancer has extensively spread beyond the chest.
Treatment of lung cancer
Lung cancer is typically treated through a team approach in which surgical oncologists, thoracic surgeons (general surgeons), radiation and medical oncologists, pulmonary specialists and pain and palliative-care specialists work together to deliver treatment. The team works with a treatment plan based on the type and stage of the cancer, overall health of the patient and the patient’s treatment preferences. For example, non-small cell lung cancers are usually treated using one or a combination of radiotherapy, surgery, chemotherapy and targeted drugs while small cell lung cancers are often treated using radiotherapy and chemotherapy.
1. Surgery for lung cancer
Surgical operation to remove a tumor is generally used to treat limited-stage lung cancer, with about 10-35 percent of lung cancer usually removed surgically. The surgical procedure selected depends on the type, size and location of the tumor. For example, wedge resection is used to remove small sections of lung tissue containing the tumor while segmental resection is used to remove larger portions of lung tissue, though not entire lobes. Lobectomy is the removal of an entire lobe while pneumonectomy is the removal of an entire lung. In some cases, lymphadenectomy is done to remove affected lymph nodes. Lung cancer surgery is a major procedure that requires hospitalization, general anesthesia and follow-up care. After the procedure, patients may experience shortness of breath, difficulty breathing, weakness and pain. The surgery also comes with risks such as infection, bleeding or side effects of general anesthesia.
The use of drugs to kill or prevent multiplication of cancer cells is called chemotherapy. The drugs can be administered alone, in combination with surgery or together with radiotherapy. Both SCLC and NSCLC can be treated with chemotherapy, though it is the treatment of choice for most cases of SCLC because the tumors are usually diagnosed when they have widely spread. There are several drugs that have been used for lung cancer, but the class known as platinum-based has shown more efficacy. The drugs may be administered as pills, intravenous infusions or a combination of the two for several weeks or months in an outpatient setting. Unfortunately, chemotherapy may result in a number of unpleasant side effects such as nausea, diarrhea, vomiting, hair loss, weight loss, fatigue, bruising and mouth sores. The side effects can be prevented or treated using some drugs, but most of them will disappear as the body recovers.
3. Targeted drug therapy
Certain drugs can be targeted to the specific genetic changes promoting tumor growth. For example, the drugs gefitinib (Iressa) and erlotinib (Tarceva) inhibit tumor cell division by targeting the proteins involved in the division. Other drugs commonly used are ceritinib (Zykadia), crizotinib (Xalkori), ramucirumab (Cyramza), nivolumab (Opdivo), bevacizumab (Avastin) and afatinib (Gilotrif). Targeted drugs are frequently used in combination with chemotherapy for maximum effect.
Radiotherapy can be safely and effectively employed to treat both SCLC and NSCLC. During radiotherapy, high-powered energy beams (such as protons and X-rays) are used to kill cancer cells. The radiation can be delivered from a machine placed outside the body (external beam radiotherapy) or from a source surgically placed inside the body (brachytherapy). Radiotherapy is the treatment of choice for cancers that cannot be removed surgically, for advanced stage cancers that have spread to lymph nodes, trachea and other areas, for people who reject surgery, and for lung cancer in people with conditions that make surgery unsafe. Radiotherapy can be curative, palliative (for symptoms relief) or an adjuvant therapy (used in combination with chemotherapy or surgery). Side effects of radiotherapy for lung cancer include fatigue, nausea, diarrhea, vomiting and skin irritation. The side effects generally improve after treatment has ended.
To cope with lung cancer and recover quickly after treatment, you should:
- Stop smoking and reduce exposure to tobacco smoke.
- Use supplemental oxygen when experiencing shortness of breath.
- Find a comfortable position when you have difficulty breathing.
- Listen to music, meditate, say a prayer, visit a favorite vacation spot or engage in activities that make you relax.
- Practice focusing your breath to improve breathing problems.
- Save your energy for important activities to avoid fatigue.
- If shortness of breath persists or symptoms get worse, inform your doctor.