Lung Cancer

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Excluding skin cancer, lung cancer has been the most common cancer in the world for several decades. It is also the most common cause of death from cancer.

The likelihood of developing lung cancer increases significantly with age, with research from the American Cancer Society showing that approximately 2 out of 3 people diagnosed are 65 years or older. Despite the very serious prognosis of lung cancer, some people with earlier stage cancers can be cured.

Read on to find out more about the causes, types and symptoms of this disease. Prevention is key when it comes to lung cancer, so included are some pointers to help you prevent this cancer.

If you are concerned that you might have lung cancer, there is information about the diagnostic tests your doctor might conduct, as well as the treatment options available.

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Typically, there are no signs or symptoms in the earliest stages of lung cancer. Once it develops, most people with lung cancer have one or more of these symptoms:

  • A new cough that doesn't go away
  • Coughing up blood or mucus
  • Wheezing
  • Chest pain
  • Shortness of breath
  • Trouble breathing
  • Headaches and fever
  • Discomfort when swallowing
  • Hoarseness
  • Poor appetite and weight loss

If the cancer has spread beyond the lungs, it can cause other symptoms such as bone pain if it has spread to your bones.

Many of these warning signs can also be caused by other conditions. See your doctor if you have symptoms so that the cause of your problem can be found, diagnosed and properly treated.

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Lung cancer is a type of cancer that starts in the lungs. Your lungs are 2 sponge-like organs found in your chest that essentially take in oxygen when you inhale and release carbon dioxide when you exhale.

Lung cancers almost always start in the cells lining the bronchi – the tubular, branching airways of the lungs. They are thought to initially produce pre-cancerous changes in the lung, but over time the abnormal cells acquire other gene changes, which cause them to progress to true cancer.

At some point, cells from the cancer may break away from the original tumor and spread (metastasise) to other parts of the body, including the liver, bones, adrenal glands and brain. Lung cancer is often a life-threatening disease because it tends to spread in this way even before it can be detected on an imaging test such as a chest x-ray.

There are more than 20 identified types of cancerous tumors that originate in the lung itself. However, lung cancers are divided into two main types, based on how their cells look under the microscope: non-small cell lung cancer and small cell lung cancer.

Non-small cell lung cancer may be localised, which means that it is limited to the lung or that it hasn't spread beyond the chest. Small cell lung cancer is rarely localised, even when it is detected early. Knowing whether the cancer has spread is critical, because it affects treatment decisions. See the section Types of Lung Cancer for more information.

What causes lung cancer?

Smoking causes the majority of lung cancers — both in smokers and in those exposed to second-hand smoke. However, more and more lung cancers are being diagnosed in people who have never smoked.

Medical experts at Mayo Clinic believe smoking causes lung cancer by damaging the cells that line the lungs. Inhaling cigarette smoke, which is full of cancer-causing substances (carcinogens), causes changes in the lung tissue to take place almost immediately. At first your body may be able to repair this damage, but with repeated exposure, normal cells that line your lungs are increasingly damaged. Over time, the damage causes cells to act abnormally and to eventually develop into cancer.

Lung cancer in non-smokers can be caused by exposure to radon, secondhand smoke, air pollution, or other factors. Workplace exposures to asbestos or certain other chemicals can also cause lung cancers in some people who do not smoke.

Types of Lung Cancer

There are 2 main types of lung cancer: small cell lung cancer and non-small cell lung cancer.

  • Small cell lung cancer: Small cell lung cancer is the most aggressive form of lung cancer and accounts for approximately 15% of all lung cancers. It is extremely rare for someone who has never smoked to have small cell lung cancer. It typically originates in the bronchi near the centre of the chest, and spreads very quickly beyond the lung, usually before any symptoms appear. For most patients with this type of cancer, the disease has spread by the time it is diagnosed. This makes it almost impossible to cure with surgery. However, it can be managed with chemotherapy or radiation therapy.
  • Non-small cell lung cancer: Non-small cell lung cancer is an umbrella term for several types of lung cancers that behave in a similar way. They also respond to treatment similarly. Non-small cell lung cancer is more likely than small cell cancer to be localised at the time of diagnosis, and it is also more likely to be treatable with surgery. Non-small cell lung cancer accounts for about 85% of all lung cancers. There are three common types of non-small cell lung cancer:
    • Adenocarcinoma: This is the most widespread type of lung cancer. Although it is linked to smoking, it is the most common type of lung cancer in nonsmokers. It is also the most common form of lung cancer in women and in people younger than 45. It tends to develop along the outer edges of the lungs in the smaller airways. It's commonly a mixed type of tumor and may cause no symptoms initially.  
    • Squamous cell carcinoma: This type of lung cancer tends to develop from the cells that line the airways and form a mass near the centre of the lungs. This type of cancer occurs more commonly in men and in smokers. It's the easiest to detect early, since its distinctive cells are likely to show up in tests. It also tends to be most curable if found early because it spreads relatively slowly and often does not spread outside of the lung.
    • Large cell carcinoma: Large cell carcinomas are a group of cancers with large, abnormal-looking cells that, like adenocarcinoma, tend to develop along the outer edges of the lungs. They are the least common of the non-small cell lung cancers. However, this type of cancer has a high tendency to grow and spread quickly, which can make it harder to treat.
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Based on your symptoms and risk factors, such as your smoking history and exposure to cancer-causing agents, your doctor may order a number of tests to look for cancerous cells. In order to diagnose lung cancer, he or she may recommend any of the below tests.

  • Imaging tests: In most cases, a chest X-ray will be done first to reveal any abnormal masses or tumors. A computerised tomography (CT) scan may also be recommended to reveal small lesions in your lungs that might not be detected on an X-ray. Combining these creates a more detailed image of the lungs, allowing doctors to confirm the size and location of a mass or tumor.
  • Sputum cytology:  For this test, a sample of sputum (mucus you cough up from the lungs) is looked at under a microscope to see if it contains cancer cells. This test is more likely to help find cancers that start in the major airways of the lung, such as most small cell lung cancers and squamous cell lung cancers.
  • Biopsy: In a biopsy, a sample of abnormal lung tissue is removed and examined under a microscope in a laboratory. Your doctor can perform a biopsy in a number of ways, however it is most often done through bronchoscopy, in which a tube-like instrument is passed down the throat and into the lungs. A biopsy sample may also be taken from lymph nodes or other areas where cancer has spread, such as your liver. If the tissue contains cancer cells, the type of cancer can be determined by the way the cells look under the microscope.

Stages of lung cancer

Once your lung cancer has been diagnosed, your doctor will often run further tests to determine the stage of your cancer. Staging tests may include imaging procedures such as CT scans, magnetic resonance imaging (MRI), positron emission tomography (PET) and bone scans. Knowing the type of cancer and its stage helps you and your doctor decide what treatment is most appropriate.

The stages for lung cancer are:

  • Stage I: Cancer is limited to the lung and hasn't spread to the lymph nodes. The tumor is generally smaller than 2 inches (5 centimetres) across.
  • Stage II: The tumor at this stage may have grown larger than 2 inches, or it may be a smaller tumor that involves nearby structures, such as the chest wall, the diaphragm or the lining around the lungs. Cancer may also have spread to the nearby lymph nodes.
  • Stage III: The tumor at this stage may have grown very large and invaded other organs near the lungs. Or this stage may indicate a smaller tumor accompanied by cancer cells in lymph nodes farther away from the lungs.
  • Stage IV: Cancer has spread beyond the affected lung to the other lung or to distant areas of the body.

In addition, small cell lung cancers are sometimes divided into 2 groups: limited or extensive. Limited means the cancer involves only one lung and the nearby lymph nodes, while extensive indicates cancer has spread beyond the one lung to other areas of the chest or to distant organs.

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Once lung cancer has been diagnosed, treatment depends on the type and stage of cancer. Options typically involve one or more treatments including surgery, chemotherapy, radiation therapy or targeted drug therapy. Surgery is the main treatment for non-small cell lung cancers that have not spread beyond the chest. There are three types of surgery:

  • Wedge resection: This removes only a small part of the lung.
  • Lobectomy: This removes one lobe of the lung.
  • Pneumonectomy: This removes an entire lung.

If you undergo surgery, your surgeon may also remove lymph nodes from your chest to check if the cancer has spread. Lung cancer surgery carries risks, including bleeding and infection. Because surgery will remove part or all of a lung, breathing may also be more difficult afterwards.

  • Chemotherapy: Chemotherapy uses drugs to kill cancer cells. Depending on how far the cancer has spread, chemotherapy can be used as a first line treatment for lung cancer or as additional treatment after surgery. When the tumor has spread significantly, chemotherapy may be recommended to slow its growth, even if it cannot cure the disease.
  • Radiation Therapy: Radiation therapy uses high-powered energy beams to kill cancer cells. It is often used to treat lung cancer that has spread to the brain or bones and is causing pain. Radiation therapy can also be used alone or with chemotherapy to treat lung cancer that is confined to the chest.
  • Targeted drug therapy: Targeted therapies are newer cancer treatments that work by targeting specific genetic abnormalities (mutations) in cancer cells. These therapies can derail the cancer's growth by preventing or changing chemical reactions linked to particular mutations. 
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Not all lung cancers can be prevented, however you can reduce your risk if you:

  • Stop smoking: Not smoking is the most important way to reduce your risk of getting lung cancer. If you already smoke, talk to your doctor about getting the help you need to quit. If you stop smoking before a cancer develops, your damaged lung tissue gradually starts to repair itself. No matter what your age or how long you’ve smoked, quitting may lower your risk of lung cancer and help you live longer. According to the American Cancer Society , people who stop smoking before age 50 cut their risk of dying from lung cancer in the next 15 years in half compared with those who continue to smoke.
  • Avoid second-hand smoke: Ask guests to smoke outdoors and seek out smoke-free restaurants and hotels.
  • Reduce exposure to radon: Have the radon levels in your home tested and, if needed, treated.
  • Avoid exposure to toxic chemicals at work: Take precautions to protect yourself from known cancer-causing chemicals in the workplace. Be sure to follow any proper safety procedures, such as wearing a face mask, if required.
  • Have a healthy diet: Diets full of fruit and vegetables may help protect against lung cancer in both smokers and non-smokers.
  • Exercise: Engaging in regular aerobic activity and strength training may help to reduce your risk of developing lung cancer. Speak to your doctor about an exercise plan that’s right for you.
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