A series of unfortunate events
How cancer genes create a tumor
By Richard Saltus
Illustration by John DiGianni
Dana-Farber researchers are developing "smart" drugs that target tumor growth directly, leaving surrounding healthy cells undamaged.
In the 1940s and early 1950s, Sidney Farber, MD, was achieving milestones in treating childhood leukemia, but neither he nor anyone else could explain how cancer cells form in the first place. Chemicals, radiation, and viruses were known to cause tumors, but exactly how they did so remained a mystery.
Since 1953, when scientists figured out the double-helix structure of DNA, a new view has emerged: Cancer arises when key genes in a normal cell become mutated. This allows the cell to divide in overdrive and behave abnormally, becoming essentially immortal and invading vital tissues and organs.
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How cancer genes create a tumor
Mutations – changes in DNA that cause cells to make abnormal proteins – can be triggered by such factors as environmental exposures; compounds in one's diet; aging; random copying errors in the genetic code; or malfunctioning telomeres, the caps on the ends of chromosomes that help keep them healthy.
A cancer cell contains not one but many mutations – in fact, the entire set of genes (the genome) becomes unstable. Chromosomes that carry the genes break, rearrange themselves, lose big chunks of genetic material, or make too many copies of DNA. As affected cells accumulate mutations over a period of years, they may become progressively abnormal and develop into full-blown, invasive cancers that often spread to other parts of the body (a process known as metastasis).
Some mutant cancer genes, called oncogenes, spur the cell into uncontrolled growth. Others disable the cell's brakes on growth – tumor suppressor genes, for example – or enable the cell to survive when it should die because of genetic damage.
With so much knowledge at hand, much cancer research today is aimed at developing "smart" drugs that home in on proteins resulting from these genetic abnormalities. The goal is to block them so the cells come under control again or succumb to the process of apoptosis, or "programmed cell death."
