Kidney cancer refers to a type of cancer that originates in the kidneys. The two kidneys are bean-shaped organs located on either side of the spine, just below the rib cage. Their primary function is to filter waste products from blood and regulate electrolyte balance. Kidney cancer occurs when healthy cells in one or both kidneys change and grow uncontrollably, forming a tumor. There are several types of kidney cancers including renal cell carcinoma (the most common type), transitional cell carcinoma, and Wilms' tumor (which primarily affects children). Treatment for kidney cancer may include surgery to remove the affected kidney(s), radiation therapy, chemotherapy or targeted therapy.