Defining cancer
Cancer is a term used for diseases in which abnormal cells divide without control and are able to invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems.
Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they
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 aren't 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.
Cancer statistics
A new report from the nation's leading cancer organizations shows cancer death rates decreased on average 2.1 percent per year from 2002 through 2004, nearly twice the annual decrease of 1.1 percent per year from 1993 through 2002.
Estimated new cases and deaths from cancer in the United States in 2008:
- New cases: 1,437,180 (does not include nonmelanoma skin cancers)
- Deaths: 565,650
What are the most common types of cancer?
The list of common cancer types includes cancers that are diagnosed with the greatest frequency in the United States. Cancer incidence statistics from the American Cancer Society and other resources were used to create the list. To qualify as a common cancer, the estimated annual incidence for 2008 had to be 35,000 cases or more.
The most common type of cancer on the list is nonmelanoma skin cancer, with more than 1,000,000 new cases expected in the United States in 2008. Nonmelanoma skin cancers represent about half of all cancers diagnosed in this country.
The cancer on the list with the lowest incidence is thyroid cancer. The estimated number of new cases of thyroid cancer for 2008 is 37,340.
Because colon and rectal cancers are often referred to as "colorectal cancers," these two cancer types were combined for the list. For 2008, the estimated number of new cases of colon cancer is 108,070, and the estimated number of new cases of rectal cancer is 40,740.
Kidney cancers can be divided into two major groups, renal parenchyma cancers and renal pelvis cancers. Approximately 85 percent of kidney cancers develop in the renal parenchyma, and nearly all of these cancers are renal cell cancers. The estimated number of new cases of renal cell cancer for 2008 is 46,232.
Leukemia as a cancer type includes acute lymphoblastic (or lymphoid) leukemia, chronic lymphocytic leukemia, acute myeloid leukemia, chronic myelogenous (or myeloid) leukemia, and other forms of leukemia. It is estimated that more than 44,270 new cases of leukemia will be diagnosed in the United States in 2008, with chronic lymphocytic leukemia being the most common type (approximately 15,110 new cases).
The following table gives the estimated numbers of new cases and deaths for each common cancer type:
| Cancer Type | Estimated New Cases | Estimated Deaths |
| Bladder | 68,810 | 14,100 |
| Breast (Female - Male) | 182,460 -- 1,990 | 40,480 - 450 |
| Colon and Rectal (combined) | 148,810 | 49,960 |
| Endometrial | 40,100 | 7,470 |
| Kidney (Renal Cell) | 46,232 | 11,059 |
| Leukemia (all) | 44,270 | 21,710 |
| Lung (including bronchus) | 215,020 | 161,840 |
| Melanoma | 62,480 | 8,420 |
| Non-Hodgkin Lymphoma | 66,120 | 19,160 |
| Pancreatic | 37,680 | 34,290 |
| Prostate | 186,320 | 28,660 |
| Skin (nonmelanoma) | >1,000,000 | <1,000 |
| Thyroid | 37,340 | 1,590 |
Source: U.S. National Institutes of Health, National Cancer Institute
Last Editorial Review: 7/23/2008
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