Cancer is a disease which can spread quickly and impact all of the body's major organs and functions. But cancer begins with the tiniest, most basic unit of life: the cells.

What happens that makes normal cells become cancer cells? Normal, healthy cells grow and divide to form new cells as the body needs them. When normal cells grow old or become damaged, they die, and new cells take their place.

Sometimes, this orderly process goes wrong. New cells form when the body does not need them, and old or damaged cells do not die as they should. The build-up of extra cells often forms a mass of tissue called a growth or tumor. Cancer types can be grouped into broader categories.

The Main Categories of Cancer

  • Carcinoma: Cancer that begins in the skin or in tissues that line or cover internal organs.
  • Sarcoma: Cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
  • Leukemia: Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
  • Lymphoma and Myeloma: Cancers that begin in the cells of the immune system.
  • Central Nervous System Cancers: Cancers that begin in the tissues of the brain and spinal cord.

Benign or Malignant?

Tumors can be either benign or malignant. Benign tumors aren't cancer. Malignant ones are. Benign tumor cells are usually not as harmful as malignant tumor cells. Benign cells are rarely a threat to life and usually do not need to be removed. Benign tumors do not invade the tissues around them and do not spread to other parts of the body.

How Cancer Spreads

Cancer cells can spread to other parts of the body through the blood and lymph systems. Cancer cells spread by breaking away from the original tumor. They enter blood vessels or lymph vessels, which branch into all the tissues of the body. The cancer cells attach to other organs and form new tumors that may damage those organs. The spread of cancer is called metastasis.


Screening tests can help find cancer at an early stage, before symptoms appear. When abnormal tissue or cancer is found early, it may be easier to treat or cure. It is important to remember that when your doctor suggests a screening test, it does not always mean he or she thinks you have cancer. Screening tests are done when you have no cancer symptoms. There are different kinds of screening tests.

  • Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease. A history of the patient's health habits and past illnesses and treatments will also be taken.
  • Laboratory tests: Medical procedures that test samples of tissue, blood, urine, or other substances in the body.
  • Imaging procedures: Procedures that make pictures of areas inside the body.
  • Genetic tests: Tests that look for certain gene mutations (changes) that are linked to some types of cancer.

Browse Our Free Senior Care Guides