Lung Cancer Basics

What is lung cancer? Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope. (Source: National Cancer Institute. Lung Cancer.)

Cancer Cells

Cancer begins in cells, the building blocks that make up all tissues and organs of the body, including the lungs. Normal cells in the lungs and other parts of the body grow and divide to form new cells as they are needed. When normal cells grow old or get damaged, they die, and new cells take their place. Sometimes, this process goes wrong. New cells form when the body doesn’t need them, and old or damaged cells don’t die as they should. The buildup of extra cells often forms a mass of tissue called a growth or tumor.

Tumors in the lung can be benign (not cancer) or malignant (cancer):

Benign tumors:

  • Are rarely a threat to life
  • Don’t invade the tissues around them
  • Don’t spread to other parts of the body
  • Usually don’t need to be removed

Malignant tumors (lung cancer):

  • May be a threat to life
  • Can invade nearby organs and tissues
  • Can spread to other parts of the body
  • Often can be removed but may grow back

Lung cancer cells can spread by breaking away from a lung tumor. They can travel through blood vessels or lymph vessels to reach other parts of the body. After spreading, cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues.

When lung cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary (original) tumor. For example, if lung cancer spreads to the bones, the cancer cells in the bones are actually lung cancer cells. The disease is metastatic lung cancer, not bone cancer. For that reason, it is treated as lung cancer, not bone cancer.

Types of Lung Cancer

The most common types are named for how the lung cancer cells look under a microscope:

  • Small cell:The cells ofsmall cell lung cancerlook small under a microscope. About 1 of every 8 people with lung cancer has small cell lung cancer.
  • Non-small cell:The cells ofnon-small cell lung cancerare larger than the cells of small cell lung cancer. Most (about 7 of every 8) people diagnosed with lung cancer have non-small cell lung cancer. It doesn’t grow and spread as fast as small cell lung cancer, and it’s treated differently.

Staging Tests

After you learn that you have lung cancer, you may need staging tests to help with decisions about treatment. Staging tests can show the stage (extent) of lung cancer, such as whether cancer cells have spread to other parts of the body.

When lung cancer spreads, cancer cells are often found in nearby lymph nodes. Lung cancer cells can spread from the lung to almost any other part of the body, such as the brain, bones, other lung, liver, or adrenal glands.

Staging tests may include...

  • CT scan: An x-ray machine linked to a computer takes a series of detailed pictures of your chest, abdomen, brain, or other parts of your body. You’ll receive contrast material by injection into a blood vessel in your arm or hand. For a CT scan of the abdomen, you may receive contrast material by mouth also. The contrast material makes abnormal areas easier to see. The pictures from a CT scan can show the lung tumor’s size. The pictures can also show cancer that has spread to your liver, adrenal glands, brain, or other organs.
  • PET scan: Your doctor may use a PET scan to get a better view of the tumor in the lung or to find cancer that has spread. You’ll receive an injection of a small amount of radioactive sugar. A machine makes computerized pictures of the sugar being used by cells in the body. Because cancer cells use sugar faster than normal cells, areas with cancer cells look brighter on the pictures.
  • MRI: A strong magnet linked to a computer is used to make detailed pictures of your head or spine. An MRI can show whether cancer has spread to these areas. Sometimes contrast material is used to make abnormal areas show up more clearly on the picture.
  • Bone scan: A small amount of a radioactive substance will be injected into a blood vessel. The radioactive substance travels through your bloodstream and collects in the bones. A machine called a scanner detects and measures the radiation. The scanner makes pictures of your bones. Because higher amounts of the radioactive substance collect in areas where cancer is present, the pictures can show cancer that has spread to the bones.
  • Other tests may be needed. For example, your doctor may remove samples of lymph nodes or other tissues to see whether lung cancer has spread.

Questions you may want to ask your doctor about tests

  • What type of lung cancer do I have?
  • Has the cancer spread from the lung? If so, to where?
  • May I have a copy of test results?

Stages

The stage of lung cancer depends mainly on...

  • The size of the lung tumor
  • How deeply the tumor has invaded nearby tissue, such as the chest wall
  • Whether lung cancer cells have spread to lymph nodes or other parts of the body
Stages of Non-small Cell Lung Cancer.  Doctors describe the stages of non-small cell lung cancer using the Roman numerals I, II, III, and IV. Stage I is early-stage cancer, and Stage IV is advanced cancer that has spread to other parts of the body, such as the bones.  You can find pictures of the stages and other information on NCI's website at http://www.cancer.gov/cancertopics/types/lung.
  • Occult Stage Lung Tumor
    • Tumor cells are found in sputum, but CT scans and other imaging tests don't show a lung tumor.
  • Stage 0 Lung Tumor
    • Abnormal cells are found only in the innermost lining of the lung. The tumor has not grown through this lining. A Stage 0 tumor is also called carcinoma in situ. It is not an invasive cancer.
  • Stage I Lung Cancer
    • The lung tumor is an invasive cancer. It has grown through the innermost lining of the lung into deeper lung tissue. The tumor is surrounded by normal tissue, and it doesn't invade nearby tissues, such as the chest wall.
    • The tumor is no more than 5 centimeters (about 2 inches) across. Cancer cells are not found in nearby lymph nodes.
  • Stage II Lung Cancer
    • The lung tumor is smaller than 7 centimeters across, and cancer cells are found in nearby lymph nodes.
    • Or, cancer cells are not found in nearby lymph nodes. The lung tumor is more than 5 centimeters across, or it invades nearby tissues, such as the chest wall, diaphragm, pleura, main bronchus, or tissue that surrounds the heart. More than one malignant tumor may be found within the same lobe of the lung.
  • Stage III Lung Cancer
    • The tumor may be any size. More than one malignant tumor may be found within the lung.
    • Cancer cells may be found in lymph nodes on either side of the chest or the neck. The tumor may have invaded nearby organs, such as the heart, esophagus, or trachea.
  • Stage IV Lung Cancer
    • Malignant tumors are found in both lungs. Or, the lung cancer has spread to other parts of the body, such as the brain, bones, liver, or adrenal glands. Or, cancer cells are found in fluid between the two layers of pleura. 
Stages of Small Cell Lung Cancer.  Most doctors describe the stages of small cell lung cancer with two stages:
  • Limited stage: Cancer is found only on one side of the chest.
  • Extensive stage: Cancer is found in the lung and also in tissues on the other side of the chest. Or, lung cancer is found in distant organs, such as the brain, or in fluid between the two layers of pleura.
Instead of limited and extensive stage, some doctors describe the stages of small cell lung cancer using the Roman numerals I, II, III, and IV. (See Stages of Non-small Cell Lung Cancer above.)

Treatment

The treatment that's right for you depends mainly on the type and stage of lung cancer. You may receive more than one type of treatment.  Click here to learn more about treatment and the treatment process.


Source: National Cancer Institute.  What You Need To Know About™ Lung Cancer.