Tuesday, August 10, 2010
What is cancer?
Cancer is a group of many related diseases. All cancers begin in cells, the building blocks that make up tissues. Cancer that arises from organs and solid tissues is called a solid tumor. Cancer that begins in blood cells is called leukemia, multiple myeloma, or lymphoma.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old and die, 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.
The extra cells form a mass of tissue, called a growth or tumor. Tumors can be either benign (not cancerous) or malignant (cancerous). Benign tumors do not spread to other parts of the body, and they are rarely a threat to life. Malignant tumors can spread (metastasize) and may be life threatening.
What is primary cancer?
Cancer can begin in any organ or tissue of the body. The original tumor is called the primary cancer or primary tumor. It is usually named for the part of the body or the type of cell in which it begins.
What is metastasis, and how does it happen?
Metastasis means the spread of cancer. Cancer cells can break away from a primary tumor and enter the bloodstream or lymphatic system (the system that produces, stores, and carries the cells that fight infections). That is how cancer cells spread to other parts of the body.
When cancer cells spread and form a new tumor in a different organ, the new tumor is a metastatic tumor. The cells in the metastatic tumor come from the original tumor. This means, for example, that if breast cancer spreads to the lungs, the metastatic tumor in the lung is made up of cancerous breast cells (not lung cells). In this case, the disease in the lungs is metastatic breast cancer (not lung cancer). Under a microscope, metastatic breast cancer cells generally look the same as the cancer cells in the breast.
Where does cancer spread?
Cancer cells can spread to almost any part of the body. Cancer cells frequently spread to lymph nodes (rounded masses of lymphatic tissue) near the primary tumor (regional lymph nodes). This is called lymph node involvement or regional disease. Cancer that spreads to other organs or to lymph nodes far from the primary tumor is called metastatic disease. Doctors sometimes also call this distant disease.
The most common sites of metastasis from solid tumors are the lungs, bones, liver, and brain. Some cancers tend to spread to certain parts of the body. For example, lung cancer often metastasizes to the brain or bones, and colon cancer frequently spreads to the liver. Prostate cancer tends to spread to the bones. Breast cancer commonly spreads to the bones, lungs, liver, or brain. However, each of these cancers can spread to other parts of the body as well.
Because blood cells travel throughout the body, leukemia, multiple myeloma, and lymphoma cells are usually not localized when the cancer is diagnosed. Tumor cells may be found in the blood, several lymph nodes, or other parts of the body such as the liver or bones. This type of spread is not referred to as metastasis.