Cancer is a group of diseases where abnormal cells develop and begin to grow out of control. Often, these abnormal cells are recognized by the body’s immune system and destroyed. However, this abnormal growth can sometimes develop into masses or tumors that can continue to grow and spread throughout the body. Cancer can also develop in blood cells and doesn’t usually form solid tumors.
Cancer occurs when changes happen to the body's genes responsible for controlling how cells function, including how they grow and divide. As cancers continue to grow, additional genetic changes can happen.