Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body.

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.

Tumor cells can be benign (not cancer) or malignant (cancer). Benign tumor cells are usually not as harmful as malignant tumor cells:

• Benign lung tumors
  • are rarely a threat to life
  • usually do not need to be removed
  • do not invade the tissues around them
  • do not spread to other parts of the body
  
  
• Malignant lung tumors
  • may be a threat to life
  • may grow back after being removed
  • can invade nearby tissues and organs
  • can spread to other parts of the body

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.

See "Staging" ¹ for information about lung cancer that has spread.

Glossary Terms

Not cancerous. Benign tumors may grow larger but do not spread to other parts of the body. Also called nonmalignant.

A thin tube that carries lymph (lymphatic fluid) and white blood cells through the lymphatic system. Also called lymphatic vessel.

Cancerous. Malignant tumors can invade and destroy nearby tissue and spread to other parts of the body.

The spread of cancer from one part of the body to another. A tumor formed by cells that have spread is called a “metastatic tumor” or a “metastasis.” The metastatic tumor contains cells that are like those in the original (primary) tumor. The plural form of metastasis is metastases (meh-TAS-tuh-SEEZ).

An abnormal mass of tissue that results when cells divide more than they should or do not die when they should. Tumors may be benign (not cancer), or malignant (cancer). Also called neoplasm.