Each of the approximately 100 different types of cancer begins with a single cell becoming abnormal and reproducing, according to the American Cancer Society. If left undetected, this growing population of malignant cells often spreads and can be fatal.
Normal cells grow and divide for a set period of time before self-terminating. They also tend to remain inside the organs where they originally grew. Cancer cells follow a different pattern, according to the American Cancer Society. In a precancerous cell, the normal mechanism for terminating cell division is disabled, leading the cell to continue dividing without pause. In some cancers, this growth forms a mass known as a tumor.
As the tumor grows, it signals the body to provide it with blood vessels that support continued growth, notes the American Cancer Society. Eventually, the tumor breaks out of its surrounding tissues and may begin to invade nearby organs. As it spreads, the growth may slough off cells into the blood or the lymphatic system; these rogue cells circulate to new cell beds and begin growing new tumors. Many factors contribute to the onset of cancer, including radiation exposure, mutagens or carcinogens in the environment and smoking. A propensity to develop cancer can also be inherited from parents.