Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body. Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, 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 cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor. Not all tumors are cancer.

Tumors can be benign or malignant:

• Benign tumors are not cancer:

  • They are rarely life threatening.

  • Usually, benign tumors can be removed, and they seldom grow back.

  • Cells from benign tumors do not spread to tissues around them or to other parts of the body.

• Malignant tumors are cancer:

  • They are generally more serious and may be life threatening.

  • Malignant tumors usually can be removed, but they can grow back.

  • Cells from malignant tumors can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the bloodstream or lymphatic system. That is how cancer cells spread from the original cancer (the primary tumor) to form new tumors in other organs. The spread of cancer is called metastasis. Different types of cancer tend to spread to different parts of the body.

Glossary Terms

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

The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels (a network of thin tubes that carry lymph and white blood cells). Lymphatic vessels branch, like blood vessels, into all the tissues of the body.

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).

The original tumor.

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 cancerous), or malignant (cancerous). Also called neoplasm.