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.

Tumors can be benign or malignant:

• Benign tumors are not cancer:
  • Benign tumors are rarely life-threatening.
  • Most benign tumors can be removed. They usually do not grow back.
  • Benign tumors do not invade the tissues around them.
  • Cells from benign tumors do not spread to other parts of the body.

• Malignant tumors are cancer:
  • Malignant tumors are generally more serious than benign tumors. They may be life- threatening.
  • Malignant tumors often can be removed. But sometimes they grow back.
  • Malignant tumors can invade and damage nearby tissues and organs.
  • Cancer cells can break away from a malignant tumor and spread to other parts of the body. Cancer cells spread by entering the bloodstream or the lymphatic system. The cancer cells form new tumors that damage other organs. The spread of cancer is called metastasis.

When colorectal cancer spreads outside the colon or rectum, cancer cells are often found in nearby lymph nodes. If cancer cells have reached these nodes, they may also have spread to other lymph nodes or other organs. Colorectal cancer cells most often spread to the liver.

When cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the original tumor. For example, if colorectal cancer spreads to the liver, the cancer cells in the liver are actually colorectal cancer cells. The disease is metastatic colorectal cancer, not liver cancer. For that reason, it is treated as colorectal cancer, not liver cancer. Doctors call the new tumor "distant" or metastatic disease.

Glossary Terms

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

A rounded mass of lymphatic tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymph (lymphatic fluid), and they store lymphocytes (white blood cells). They are located along lymphatic vessels. Also called lymph gland.

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).

Having to do with metastasis, which is the spread of cancer from the primary site (place where it started) to other places in the body.

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.