The prostate is the walnut shaped gland in males located between the bladder and the urethra that is involved in the liquefaction of the male ejaculate. The gland is made up of secretory cells with a surrounding connective tissue stroma. Prostate cancer is the transformation of these secretory cells into malignant cells that have the potential to grow more rapidly and spread outside of the prostate. Prostate cancer will often start out localized in the prostate, but can then spread into adjacent tissue structures and lymph nodes if not detected early. The most common site of metastatic disease is the bone, but it can also spread to the lung, liver and other organs.