Kidney cancer is a disease in which cancer cells grow in the kidneys. The kidneys are two bean-shaped organs. They are located just above the waist, on each side of the spine. Their main function is to filter the blood and produce urine.

There are two main types of kidney cancer: Wilms tumor, which occurs mainly in children, and renal cell carcinoma in adults. The cells that line the ureter may also give rise to transitional cell cancer, and the connective tissues of the kidney may produce sarcomas, which are rare.

Cancer Cell Growth
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Cancer occurs when cells in the body divide without control or order. Normally, cells divide in a regulated manner. If cells keep dividing uncontrollably when new cells are not needed, a mass of tissue forms, called a growth or tumor. The term cancer refers to malignant growths. These growths can invade nearby tissues. Cancer that has invaded nearby tissues can then spread to other parts of the body.

It is not clear exactly what causes these problems in the cells, but it is probably a combination of genetics and environment.