[Conservativegreatgrandma]

What is cancer? Is it caused by a germ, or a virus or a fungus? What is it?

[Pharmboy]

Cancer is a condition where the cells lose their normal system of checks on their own growth. It can be caused by any number of things that affect the genetic makeup of the cell: viruses, chemicals ("carcinogens"), sunlight, radiation and others. The final common pathway is a cell that is out of control and lives forever.

The immune rsponse to cancer cells in the body is complex, and not just a case of our immune systems getting rid of the cancer cells when they arise; for example, people with immune disorders/deficiencies do not necessarily get more cancers than normals.