We don't catch it from someone. It isn't an unlucky break. It is primarily the results of years of malnutrition from poor eating habits, resulting in a weak immune system from lack of proper nutrition and a severely toxic state in the body. Some forms of cancer are the results of exposure to toxic chemicals and radiation. Cells in our bodies have a life-span.
Cancer cells are some of our own cells that have mutated and refuse to die.
They can create their own blood supply lines, and steal nutrition from the surrounding cells. They choke off the life of organs and sections of the body. That sounds too general to be true, but it is. Well, that combined with your own personal weaknesses. That's why it will show up in the lungs for one person and in the liver for another.