Flexi Says: Cancer is a disease that affects almost all animals. Cancer occurs when the cell cycle is no longer regulated and cells divide out of control. Some of the mechanisms that regulate cell division and stop old cells from dividing are common throughout the animal kingdom. When these mechanisms become interrupted, tumors can form. Some cancers are much more common in humans than in other mammals, including lung and prostate cancer. However, in general, cancer has been around long before humans evolved. The earliest known description of cancer in a human was documented in Egypt around 3000 B.C.E.