The Gene Factor:
Genes and Cancer

Cancer begins with a single cell. The cell may be damaged when a person is at an early age. That is, there may be mutations on one or more of the genes in the cell. The mutations may even have been inherited. Genes may also mutate as the result of a factor in the environment, like overexposure to the sun or smoking. But the net result of the mutation is that the cell's growth and division cycle are affected.

Most of us are familiar with mitosis as the way cells divide. Mitosis is just one part of the cell cycle that also includes the "G1" phase in which the cell increases in size and gets ready to copy its DNA; the "S phase" in which the copying takes place and chromosomes are duplicated; the "G2 phase," a gap phase; and the "M phase" or mitosis. The control of the cell cycle lies with genes in the cell. From these genes arise two opposing forces: those supplied by oncogenes and their parent genes, proto-oncogenes, which promote cell growth and division and those tumor suppressor genes that inhibit growth and division. Think of it as a battle for cell control. If the oncogenes are in control cell division continues unabated; suppressor genes keep the division in check. But if mutations alter the balance in favor of the oncogenes, cancer is the result.

Some examples of oncogenes:

• erb-B — brain and breast cancers
• Ki-ras — lung, ovarian, colon and pancreatic cancer
• N-ras — leukemias
• Bcl-1 — breast, head, and neck cancers