Even though there are more than 100 different types of cancer, each one begins in your cells, your body's basic building blocks. Cancer begins when cells divide and grow uncontrollably, forming malignant tumors that can spread to other parts of the body through the blood stream or lymph systems. Early detection and treatment is key to fighting cancer. For women, the most common forms of cancer are breast, colorectal and lung. For men the most common cancers are prostate, lung and colorectal, and for children leukemia, brain tumors and lymphoma. Learn more about preventing and treating all types of cancer with expert advice from Sharecare.