By Dennis Thompson
(HealthDay News) -- Why one person gets cancer and another doesn't is often unclear. Less mysterious, though, is how cancer gets started.
Cancer begins in cells, considered the building blocks of tissues that make up the body's organs. As the U.S. National Cancer Institute explains it, cells normally grow and divide, forming new cells as needed to replace old ones that die off. It's an orderly process, but it sometimes goes awry: New cells form when the body doesn't need them, and old cells don't die when they should.
The result is a mass of tissue known as a tumor. But a tumor does not automatically indicate cancer.
Benign tumors are not cancerous. They usually can be removed, they seldom grow back, they do not spread to other parts of the body and they are rarely life-threatening.
Malignant tumors, however, are cancerous. They also can be life-threatening. These tumors can often be removed, though they sometimes grow back, or recur. Malignant tumors can damage nearby tissues and organs and can spread, or metastasize, to other parts of the body.
This happens when cancer cells break away from the original, or primary, tumor and enter the bloodstream or the lymphatic system, which produces and carries lymph and white blood cells to all parts of the body. This allows the cancer cells to travel far from the primary tumor, invade other organs and form new tumors.
Even though a cancer has spread, it retains its original name. For example, if a prostate cancer spreads to the bones, the cancer cells in the bones are actually prostate cancer cells. The disease is not bone cancer, but rather metastatic prostate cancer or a "distant" tumor. It also would be treated as prostate cancer, not bone cancer.
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