Understanding What Cancer Is

How Does Cancer Start?

Cancer starts due to changes to our genes. These changes affect how the cells function – specifically how they grow and divide.

What specifically causes the cancer to start? These genetic changes can be inherited from our parents or as a result of errors which occur during cell division. When we’re exposed to the causes discussed previously, this can cause changes to the DNA.

Also, genetic changes tend to affect three types of genes:

  1. Proto-oncogenes: genes that are involved in normal cell division, when altered or more active than usual, they may cause cancer. This allows cells to grow when they should have died.
  2. Tumor suppressor genes: involved in cell growth and division, when these genes have alterations, they tend to divide uncontrollably.
  3. DNA repair genes: genes that fix damaged DNA, when mutated, these genes may cause mutations in other genes, which may cause cancerous cells.

How Does Cancer Spread?

Cancer that spreads is said to have metastasized. Metastatic cancer is cancer that has spread from the primary cancer to another area of the body. Cancer typically spreads because cells break free from the tumor, traveling to other parts of the body through the bloodstream or the lymph system.

When cancer cells travel through the lymph system, the cells are likely to settle into lymph nodes or in organs. When cells travel through the bloodstream, however, they can go anywhere in the body. Fortunately, many of these cancer cells will die, but some may settle into a new area and form new tumors.


For cancer cells to spread to different areas of the body, they must go through the following steps:

  • The cells must break off from the tumor and enter the bloodstream or lymph system, where they are carried to another part of the body.
  • The cell must attach to the wall of a blood or lymph vessel to move into a new organ.
  • The cell must be able to grow in its new location.
  • The cell must be able to avoid attacks from the immune system.

If someone has breast cancer and their cancer has metastasized to the lungs, this does not mean that they have both breast cancer and lung cancer – this means that they have metastatic breast cancer. Treatment would be specific to breast cancer, as opposed to lung cancer.

Cancer is termed cancer of unknown primary when it has spread to various places, making it challenging to locate the primary location of cancer.

Cancer Cells vs. Normal Cells

Normal cells grow and mature at a normal pattern. They are also specialized, depending on where they are in the body. For example, an epithelial cell is different than a smooth muscle cell.

Cancer cells are less specialized. This is why cancer cells may develop and divide without stopping. Cancer cells can ignore signals that normal cells receive to stop dividing. Also, according to the National Cancer Institute, “cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.”

The immune system keeps us healthy – it helps to remove damaged and abnormal cells. However, cancerous cells may be able to “hide” from the immune system. Tumor cells may actually use the immune system to grow – “with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.”

How Is Cancer Diagnosed?

  • Generally, a biopsy should be taken to achieve a proper diagnosis. A biopsy involves removing a sample of tissue so that a pathologist can review the tissue to see if the sample is cancerous. The biopsy may be achieved with a needle (needle biopsy), during an endoscopy or surgery.
  • Lab tests can help to detect signs of cancer. The specific labs that would be helpful are dependent on the type of cancer that is suspected. Your physician may order blood, urine, and other body fluids to help ascertain a diagnosis. However, labs cannot diagnose cancer without a biopsy, but it can give clues.
  • CT scans help to visualize tumors. A CT scan uses an x-ray linked to a computer to take very detailed photos.  Sometimes contrast is administered to better visualized the tumor.
  • Nuclear scans use a tracer, which is a radioactive material, that is injected into the body. The tracer flows throughout the body, collecting in bones and organs where a tumor may be. A machine detects the radioactivity. The scanner can create pictures of the bones and organs.
  • Ultrasound uses sound waves that bounce off the body. We are unable to hear these sound waves, but a computer can create a picture from these sound waves.
  • Magnetic resonance imaging, also known as MRI, uses a strong magnet linked to a computer. Very detailed photos can be created, and they can be printed.
  • PET scan also uses a tracer injection. A machine can take 3-D photos of the areas that the tracer collects in the body.
  • X-rays use very low doses of radiation to take photos of various areas of the body.

Next page: The signs and symptoms of cancer, how cancer is treated, and more “what is cancer?” education.

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