Resource: Genetic Therapy and Breast Tumors

Gene testing appears on the outside to be an easy first step toward eliminating genetic disease. Unfortunately, for many diseases like breast cancer, the path from test to cure -- or even test to treatment -- is not so straightforward.

Although some breast cancer cases appear to be the result of mutations in one or two suspected genes, greater than 90 percent of cases seem to have no hereditary link. These cases are more likely the result of environmental factors, such as poor diet or exposure to radiation and carcinogenic chemicals, are thus undetectable using genetic screens.

For some women, however, genetic testing can provide an important early risk assessment. A family history of the disease dramatically increases a woman's breast cancer risk -- by as much as threefold if a mother or sister has it -- and it is women with just such histories who most often choose to be tested.

To conduct a genetic test for breast cancer, doctors take a small tissue sample from the patient. Using restriction enzymes they extract and isolate the BRCA1 (breast cancer 1) gene from chromosome 17, and the BRCA2 gene from chromosome 13. The doctors then look for mutations, or misspellings, along each of these strands. Scientists believe it is these misspellings that inhibit the genes' ability to control tissue growth in the breast.

Studies show that the likelihood of the average woman's getting breast cancer sometime in her life is about 12 percent. However, if genetic tests show a mutation in either the BRCA1 or the BRCA2 gene, or both, her risk of getting breast cancer can jump to 85 percent.

Fortunately, a positive test for a breast cancer gene mutation only suggests a level of probability that the patient will develop breast cancer. It does not mean that she will develop the disease or that she already has it. Unfortunately, a patient's options in light of a positive test are still quite limited, since there are no proven cancer preventatives. These options will undoubtedly expand in the future.

What effect do mutations have on the growth factor receptors of cells and, ultimately, on cell growth?

What two clues led Dr. Slamon to his discovery of the relationship between oncogenes and breast tumors?

What did Dr. Slamon's experiment on hairless mice demonstrate about the effect of genetically engineered antibodies on tumors?