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Cancer

  • Posted: 10/04/2006

Understanding Cancer

Cancer begins in cells, the building blocks that form 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.
    • Generally, benign tumors can be removed, and they usually do not grow back.
    • Cells from 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.
    • Cells from malignant tumors can invade and damage nearby tissues and organs.
    • Cells from malignant tumors can spread (metastasize) to other parts of the body. Cancer cells spread by breaking away from the original (primary) tumor and entering the bloodstream or lymphatic system. The cells can invade other organs, forming new tumors that damage these organs. The spread of cancer is called metastasis.

Most cancers are named for where they start. For example, lung cancer starts in the lung, and breast cancer starts in the breast. Lymphoma is cancer that starts in the lymphatic system. And leukemia is cancer that starts in white blood cells (leukocytes).

When cancer spreads and forms a new tumor in another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if prostate cancer spreads to the bones, the cancer cells in the bones are actually prostate cancer cells. The disease is metastatic prostate cancer, not bone cancer. For that reason, it is treated as prostate cancer, not bone cancer. Doctors sometimes call the new tumor "distant" or metastatic disease.



Glossary Terms

benign (beh-NINE)
Not cancerous. Benign tumors may grow larger but do not spread to other parts of the body. Also called nonmalignant.
cell (sel)
The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.
leukemia (loo-KEE-mee-uh)
Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of blood cells to be produced and enter the bloodstream.
leukocyte (LOO-koh-site)
A type of immune cell. Most leukocytes are made in the bone marrow and are found in the blood and lymph tissue. Leukocytes help the body fight infections and other diseases. Granulocytes, monocytes, and lymphocytes are leukocytes. Also called WBC and white blood cell.
lymphatic system (lim-FA-tik SIS-tem)
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.
malignant (muh-LIG-nunt)
Cancerous. Malignant cells can invade and destroy nearby tissue and spread to other parts of the body.
metastasis (meh-TAS-tuh-sis)
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).
organ (OR-gun)
A part of the body that performs a specific function. For example, the heart is an organ.
primary tumor (PRY-mayr-ee TOO-mer)
The original tumor.
tissue (TIH-shoo)
A group or layer of cells that work together to perform a specific function.
tumor (TOO-mer)
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.