What Is Lung Cancer?

Lung cancer (like other cancers) begins with mutations in the DNA of lung cells. As these cells grow and become cancerous, they fail to carry out the functions for which they were designed. Instead, they grow out of control, eventually crowding healthy cells, tissues, and organs around them. In time, these cells may travel to other parts of the body (known as metastasis). When cancer starts somewhere else (like the stomach) and moves to the lungs, it becomes secondary lung cancer.

Veterans of the U.S. military often have an increased risk of lung cancer due to occupational exposure to risk factors or play a role in causing lung cancer.

Risk Factors and Common Causes

While smoking cigarettes is the leading cause of cancer (accounting for about 80 percent of lung cancer deaths), it is not the only factor in developing the disease. Not every person who smokes will be diagnosed with cancer, meaning more factors determine how a particular cancer grows. Certain risk factors (i.e., elements that give an individual greater odds of contracting an illness) play a part in getting lung cancer, including:

  • Cigarette smoking
  • Secondhand smoke
  • Exposure to some chemicals
  • Genetics

Elements of a person’s life that directly lead to the growth of lung tumors are known as causes of lung cancer. Known links to the development of lung cancer include:

  • Asbestos exposure
  • Cigarette smoking
  • Prolonged diesel exhaust inhalation
  • Radon exposure


Often, cancerous tumors located in the lungs are not diagnosed or treated until they cause painful symptoms that require a doctor’s visit. Chest swelling and pain, however, may be caused by tumors already in the advanced stages of NSCLC or SCLC. Of all patients, for instance, only 16 percent receive earliest-stage diagnoses.

Subsequently, recognizing the common symptoms of lung cancer can increase your chances of being diagnosed earlier, when treatments are more effective. If any of the following symptoms cause you prolonged discomfort, talk with your doctor immediately.

  • Blood in cough
  • Change in color or amount of sputum
  • Chest pain
  • Coughing
  • Hoarse voice
  • Recurrent pneumonia or bronchitis
  • Shortness of breath

Lung cancer symptoms that indicate the cancer may have spread to other parts of the body include:

  • Bleeding
  • Blood clots
  • Bone pain
  • Fatigue
  • Headaches
  • General weakness
  • Loss of appetite and weight loss
  • Muscle wasting
  • Neurological complications


Today, early screening offers veterans and their families the best chances for effective treatment. Low-dose spiral CT scans (similar to X-rays) have reduced deaths from lung cancers from 20 percent to below 16 percent. Yet, too many people neglect cancer screenings and are only tested for cancer after symptoms are present.

Generally, a doctor will conduct a physical exam and interview to determine the likelihood of lung cancer (or other diseases, like mesothelioma). Often, non-invasive tests (like CT scans) are conducted to detect the presence of cancer. Then, analyses like fluid and tissue biopsies collect samples from the patient. A laboratory will provide a positive or negative cancer result up to a few days following the test.

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Types and Stages

Lung cancer is not one, specific tumor but a group of cancers that begin in the lungs. The two major types are non-small cell lung cancer (the more common type) and small cell lung cancer (associated with cigarette smoking). Pancoast and carcinoid are other, rarer forms of the disease.

Non-Small Cell Lung Cancer

Between 80 and 85 percent of all lung cancers are classified as non-small cell lung cancer (NSCLC). Analyzing tumor cell samples under a microscope, doctors recognize three main subtypes of NSCLC. Though these tumors grow in different types of cells within the lungs, their prognoses and common treatment methods are comparable.

  • Adenocarcinoma: Tumors often start in cells that produce fluid (like mucus), often the outer lung. Most common form among smokers, nonsmokers, men, and women. Younger patients are more likely to be diagnosed with this form.
  • Large cell (undifferentiated) carcinoma: Tumors can start anywhere in the lung and are more likely to spread in a shorter amount of time.
  • Squamous cell carcinoma: Form linked to a history of smoking. Tumors often found near the center of a lung, near the bronchus (air pathway).
  • Other forms of tumors include Pancoast and carcinoid. Typically, Pancoast tumors (i.e., superior sulcus tumors) are NSCLC tumors, though this tumor cell type can be found in diseases such as tuberculosis and lymphoma. Carcinoid tumors, unlike most others, grow more slowly and consist of neuroendocrine cells. Treatment generally includes surgery as the primary treatment.

Similar to other cancers, the stages of NSCLC are organized from I to IV using Roman numerals. Stages I and II are considered early-stage, with tumors localized to one lung and/or nearby lymph nodes. Stages III and IV, however, are considered advance stage cancer. At this point, treatment options may be limited due to the spread of tumors.

Small Cell Lung Cancer

Among all lung cancers in the U.S., small cell lung cancer (SCLC) makes up about 15 percent of cases. These types of tumors generally grow and spread more quickly than NSCLC tumors but respond better to treatment using chemotherapy. Due to its relative irregularity of SCLC, the staging system classifies tumors as limited (tumors found on one side) or extensive (tumors spread beyond the chest) stage. In addition to this system, the American Joint Commission on Cancer also uses NSCLC’s staging system to give a more detailed description of metastases.

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