Cancer is essentially a collection of several different diseases that all have something to do with cells. All living things, including the human body, are made up of cells, which are extremely small units. Each person's body has billions of cells. Cancer develops when abnormal cells proliferate and spread rapidly. Cancer is not caused by bad genes people inherit from their parents; it is a complex disease that involves changes in the way our DNA codes for proteins, as well as changes in other molecules inside cells. All types of cancer are life-threatening, although some can be treated or controlled. The most effective treatment for cancer is often a combination of therapies. These include surgery to find and remove tumors before they can grow larger; chemotherapy, which uses drugs to kill cancer cells; and radiation therapy, which uses high-energy rays to destroy cancer cells. Cancer is a very complicated disease, and scientists do not know everything about how it develops. However, what we do know leads us to believe that cancer is a result of changes occurring at the molecular level inside cells. These changes cause the cell to reproduce without limit, which can lead to the formation of tumors. The word "cancer" comes from two words: karvos meaning flesh and nous meaning mind.