Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.

• Cancer can start almost anywhere in the human body, which is made up of trillions of cells.
  • Normally, human cells grow and multiply (through a process called cell division) to form new cells as the body needs them.
  • When cells grow old or become damaged, they die, and new cells take their place.
• Sometimes this orderly process breaks down, and abnormal or damaged cells grow and multiply when they shouldn’t.
  • These cells may form tumors, which are lumps of tissue.
  • Tumors can be cancerous or not cancerous (benign).
• Cancerous tumors spread into, or invade, nearby tissues and can travel to distant places in the body to form new tumors (a process called metastasis).
  • Cancerous tumors may also be called malignant tumors.
  • Many cancers form solid tumors, but cancers of the blood, such as leukemias, generally do not.
• Benign tumors do not spread into, or invade, nearby tissues.
  • When removed, benign tumors usually don’t grow back, whereas cancerous tumors sometimes do.
  • Benign tumors can sometimes be quite large, however.
  • Some can cause serious symptoms or be life threatening, such as benign tumors in the brain.

Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.

• Genetic changes that cause cancer can happen because:
  • of errors that occur as cells divide.
  • of damage to DNA caused by harmful substances in the environment, such as the chemicals in tobacco smoke and ultraviolet rays from the sun.
  • they were inherited from our parents.
• The body normally eliminates cells with damaged DNA before they turn cancerous.
  • But the body’s ability to do so goes down as we age.
  • This is part of the reason why there is a higher risk of cancer later in life.
• Each person’s cancer has a unique combination of genetic changes.
  • As the cancer continues to grow, additional changes will occur.
  • Even within the same tumor, different cells may have different genetic changes.

• A cancer that has spread from the place where it first formed to another place in the body is called metastatic cancer.
  • The process by which cancer cells spread to other parts of the body is called metastasis.
• Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer.
  • For example, breast cancer that forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer.
• Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer.
• Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
• In some cases, treatment may help prolong the lives of people with metastatic cancer.
  • In other cases, the primary goal of treatment for metastatic cancer is to control the growth of the cancer or to relieve symptoms it is causing.
• Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.