Cancer happens when normal cells in your body start to grow out of control and form a lump called a tumor. Not all tumors are cancerous, but the ones that are can spread to other parts of the body and make you sick. Cancer can happen to anyone, and there are many factors that can increase your chance of getting it, like smoking, genetics, and exposure to certain chemicals. There are different types of cancer, and they can be treated in different ways, including surgery, chemotherapy, and radiation therapy.