Cancer is a group of more than 100 different diseases characterized by the uncontrolled, abnormal growth of cells. These cells form a lump or mass called a tumor. Some cancers, however, such as blood cancers, do not form tumors. Tumors can be benign (noncancerous) or malignant (cancerous). Benign tumors may grow, but they do not spread to other parts of the body and are usually not life threatening. Malignant tumors grow and invade other tissues in the body.
Sometimes cancer will spread to the lymph nodes. A lymph node is a tiny, bean-shaped organ that filters the flow of lymph, the clear fluid that plays a role in the body’s immune system. Lymph nodes are located in clusters in different parts of the body, such as the neck, groin area, and under the arms. Cells from malignant tumors can also break away and travel to other parts of the body, where they can continue to grow. This process is called metastasis. Metastatic cancer is named for the part of the body where it started. For example, if breast cancer spreads to the lungs, it is called metastatic breast cancer, not lung cancer.
Cancer can begin almost anywhere in the body. Tumors are named for the type of cell where the cancer started. For example, carcinomas begin in the skin or tissue that covers the surface of internal organs and glands. Sarcomas begin in the connective tissue, such as muscle, fat, cartilage, or bone. Cancer types can be grouped into broader categories. The main categories of cancer include:
- Carcinoma – cancer that begins in the skin or in tissues that line or cover internal organs
- Sarcoma – cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue
- Leukemia – cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood
- Lymphoma and myeloma – cancers that begin in the cells of the immune system
- Central nervous system cancers – cancers that begin in the tissues of the brain and spinal cord
Origins of Cancer
All cancers begin in cells, the body’s basic unit of life. To understand cancer, it’s helpful to know what happens when normal cells become cancer cells.
The body is made up of many types of cells. These cells grow and divide in a controlled way to produce more cells as they are needed to keep the body healthy. When cells become old or damaged, they die and are replaced with new cells. However, sometimes this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. The extra cells may form a mass of tissue called a tumor.
Not all tumors are cancerous; tumors can be benign or malignant. Benign tumors are not cancerous. They can often be removed, and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body.
Malignant tumors are cancerous. Cells in these tumors can invade nearby tissues and spread to other parts of the body. The spread of cancer from one part of the body to another is called metastasis. Some cancers do not form tumors. For example, leukemia is a cancer of the bone marrow and blood.
A new report from the nation’s leading cancer organizations shows that, for the first time since the report was first issued in 1998, both incidence and death rates for all cancers combined are decreasing for both men and women, driven largely by declines in some of the most common types of cancer. Today, there are approximately 10.5 million Americans alive with a history of cancer.