What the prostate is
The prostate is a gland found only in males. In younger men, it is about the size of a walnut, but it can be much larger in older men. The prostate is found below the bladder. It surrounds the first part of the tube (urethra), which carries urine from the bladder to the penis. The same tube also carries semen. The prostate gland is divided into 2 lobes, to the left and the right of a central groove.
What the prostate does
The role of the prostate is to make some of the fluid that protects and nourishes sperm cells in semen, making the semen more liquid. The growth and function of the prostate depends on the male sex hormone testosterone, which is produced in the testes. Some treatments for prostate cancer work by lowering the levels of testosterone.
Several types of cells are found in the prostate, but almost all prostate cancers develop from the gland cells (the cells that make the prostate fluid that is added to the semen). As such, the information on this site refers to prostate cancer that has developed from gland cells.