There are two kidneys which are located just on either side of the spine close to the back.  The function of kidneys is to filter the blood and excrete them through the urine.

Renal Cancer

Renal cell carcinoma is the name given to cancers of the kidneys. Renal cell carcinoma can affect both men and women. Many cases of renal cell carcinoma do not produce symptoms until the disease is advanced. Symptoms may be flank pain or blood in the urine (hematuria).  Renal cell cancer can spread, or metastasize, to the lungs, bones, lymph nodes, and the brain.