Cancer is the uncontrolled growth of abnormal cells in the body. Cancer develops when the body's normal control mechanism stops working. Old cells do not die and instead grow out of control, forming new, abnormal cells. These extra cells may form a mass of tissue, called a tumor. Some cancers, such as leukemia, do not form tumors.
Cancer may occur anywhere in the body. In women, breast cancer is one of the most common. In men, it's prostate cancer. Lung cancer and colorectal cancer affect both men and women in high numbers.
Doctors divide cancer into types based on where it began. Four
main types of cancer are:
There are many other types of cancer.