Changes in the
genome that allow uncontrolled cell proliferation or cell immortality are responsible for
cancer. It is believed that the major changes in the genome that lead to cancer arise from mutations in
tumor suppressor genes. In 1997, Kinzler and
Bert Vogelstein grouped these cancer susceptibility genes into two classes: "caretakers" and "gatekeepers". In 2004, a third classification of tumor suppressor genes was proposed by Franziska Michor,
Yoh Iwasa, and
Martin Nowak; "landscaper" genes.