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Overview of Cancer

by Bruce A. Chabner, MD, Elizabeth Chabner Thompson, MD, MPH

A cancer is an abnormal growth of cells (usually derived from a single abnormal cell). The cells have lost normal control mechanisms and thus are able to expand continuously, invade adjacent tissues, migrate to distant parts of the body, and promote the growth of new blood vessels from which the cells derive nutrients. Cancerous (malignant) cells can develop from any tissue within the body.

As cancerous cells grow and multiply, they form a mass of cancerous tissue—called a tumor—that invades and destroys normal adjacent tissues. The term tumor refers to an abnormal growth or mass. Tumors can be cancerous or noncancerous. Cancerous cells from the primary (initial) site can spread throughout the body (metastasize).

Types of Cancer

Cancerous tissues (malignancies) can be divided into those of the blood and blood-forming tissues (leukemias and lymphomas) and “solid” tumors (a solid mass of cells), often termed cancer. Cancers can be carcinomas or sarcomas.

Leukemias and lymphomas are cancers of the blood and blood-forming tissues and cells of the immune system. Leukemias arise from blood-forming cells and crowd out normal blood cells in the bone marrow and bloodstream. Cancer cells from lymphomas expand lymph nodes, producing large masses in the armpit, groin, abdomen, or chest.

Carcinomas are cancers of cells that line the skin, lungs, digestive tract, and internal organs. Examples of carcinomas are cancer of the skin, lungs, colon, stomach, breasts, prostate, and thyroid gland. Typically, carcinomas occur more often in older than in younger people.

Sarcomas are cancers of mesodermal cells. Mesodermal cells normally form muscles, blood vessels, bone, and connective tissue. Examples of sarcomas are leiomyosarcoma (cancer of smooth muscle that is found in the wall of digestive organs) and osteosarcoma (bone cancer). Typically, sarcomas occur more often in younger than in older people.

Most Common Cancers in Men and Women*

Group

Cancer

Men

Prostate

Lung

Colon and rectum

Bladder

Kidney

Women

Breast

Lung

Colon and rectum

Uterus

Thyroid gland

*The most common cancers are at the top of the list, and go down in decreasing frequency. The order is based on estimates for 2013 from the American Cancer Society. Skin cancer is probably the most common cancer in both men and women, but only one type of skin cancer—melanoma—is required to be reported. How common other types are is less clear. Thus, skin cancer figures are incomplete and are therefore generally excluded from statistics.

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