A Legacy of Cancer

Jennifer Davis is working her way through college with plans to become a doctor. On the outside, Davis seems like a normal 22-year-old. But inside, she lives with the knowledge that cancer has been stalking her family for generations.

It killed her great-grandmother, her grandmother and her grandmother's sister. And then her mother was diagnosed with cancer.

That's when the family learned about a genetic test that can predict the likelihood of getting breast cancer, a cancer that can strike both men and women. The existence of this test leads to a terrible, almost unimaginable decision -- whether to surgically remove parts of your body to prevent the cancer.

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A Family Struggle

Davis' mother, Susan Davis, was diagnosed with breast cancer in 2003 and became the driving force encouraging members of her family to get tested for the gene, which took some courage. Experts estimate a million people carry the cancer risk mutation -- known as the BRCA gene -- and 97 percent don't know they have it. The stunning statistic in Davis' family is that eight out of nine members are positive for the gene.

But the Davis family is part of the 3 percent that do know. Both of Susan Davis' siblings, Linda Nicholson and Steve Halt, tested positive for the gene. And of the three siblings' children, six out of seven have the BRCA gene. (For a more detailed look, click here to view the family tree.)

"Nightline" talked to the family in two groups. The first group consisted of the more "senior" generation -- siblings Linda, Steve and Susan.

Then ABC News talked to their children, who range in age from 22 to 40 and in some cases have small children of their own. The family members were remarkably comfortable talking about their genetic bad luck.

"We're the mutant family, we all have mutated genes … so it's kind of our joke," said 40-year-old Jeff Garner. "I mean, what are you going to do?"