Lymph is a clear fluid that contains tissue waste products and immune system cells. Lymphatic vessels carry this fluid to lymph nodes (small, bean-shaped collections of immune system cells important in fighting infections). Most lymphatic vessels of the prostate lead to pelvic lymph nodes. Cancer cells can enter lymph vessels and spread out along these vessels to reach lymph nodes, where they can continue to grow. If prostate cancer cells have multiplied in the pelvic lymph nodes, they are more likely to have spread to other organs of the body as well.