Cindy McMillan was only 39 when she was diagnosed with breast cancer.
She, like others wondered, why.
"It was a real shock because I hadn't even had my baseline mamogram yet. It was kind of frightening. We grew up vegetarian, and we grew up very active, so to have a diagnosis at an early age was a mystery. No one knew why," McMillan said.
McMillan's twin sister, Susan worried too.
Was it something in the environment growing up in Virginia? Or was it in the genes, even though there was no family history of breast cancer?
So when they were asked to join in a long-term research study, the twins, along with older sibling Sally--said yes.
"Both of my sisters are into data, and both were willing to participate and willing to be data points," McMillan said.
"A researcher came out to their homes collected dust and collected finger and toenail clippings and collected hair samples, so it was quite an intensive process," McMillan said.
The Sister Study, which looks at environmental and genetic factors has been tracking 50,000 women over a 10-year period. It is being conducted by the National Institute of Health Sciences in North Carolina.
Since the study began, 2,000 sisters have been diagnosed with breast cancer.
Fortunately, most were diagnosed early.
Lead researcher Dale Sandler can't say enough about the loyalty of study participants who have been willing to share their personal information to help others.
"This is fabulous, in terms of the things we can learn from these participants," Sandler said.
The response rate is extremely high, at 95 percent -- higher than most other studies.
Thanks to a donation of close to $2 million from the Susan Komen Foundation, researchers were able to launch a second related study called the Two Sister Study which looked at not just siblings of women who came down with breast cancer at an early age but their parents too.
The expanded studies are able to look at social issues, treatment experience and lifestyle changes.
McMillan wonders if in her case, years of exposure to secondhand smoke at work may have been the trigger.
She hopes the studies will help provide clues to help predict who's at risk of developing breast cancer.
"Studies like this are immensely important. The ongoing longitudinal studies provide a wealth of knowledge that we just desperately need in this fight," said McMillan.
She is looking ahead to marking her 10-year anniversary of being cancer-free.