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. There are five main categories of cancer: Carcinomas begin in the skin or tissues that line the internal organs; Sarcomas develop in the bone, cartilage, fat, muscle or other connective tissues; Leukemia begins in the blood and bone marrow; Lymphomas start in the immune system; Central nervous system cancers develop in the brain and spinal cord.