In a cancer cell, the signals controlling growth become mutated, and a specialized cell will begin growing again (in other words, enter the cell cycle again, or "dedifferentiate"). This can be a big problem because the tools (usually the tumor suppressor genes) used to control cell growth no longer work properly. The abnormal cell may begin to divide, making more abnormal cells, and a benign tumor may form. These images show prostate tissue from a man. Cancer cells have been stained so that they appear dark in the pictures.