Like most organs, the prosate can get cancer. In short, cancer is a disease where something has caused a mutation in a cell that messes up the cell cycle. Instead of doing its normal job, the cell starts reproducing much faster than normal. The resulting mass of cells is called a tumor, and as it grows, the tumor uses more and more resources that would normally go to healthy cells. When a tumor gets large, it can start pushing against healthy tissue, causing complications. Eventually, it's possible for some cancerous cells to break off of the main tumor, and get carried away through the bloodstream. This leads to metastasis, where cancer is happening throuout the body.

Normally the cancer starts in the interior of the prostate. If it grows to the edge of the prostate, called the capsule, it might cause metastasis, so it's important to find it in the early stages.