They have inherited a mutation of the BRCA1 gene, which means proteins that normally repair DNA do not function properly. That leads to the development of cells with changes that can become cancerous.
Brown, 28, is a teacher in Aberdeen, while Andrews, 27, is an event planner for a resort in Singapore. They were both tested for the BRCA1 gene mutation after Susan Smith, their aunt, tested positive for the gene mutation in 2005.
The tests confirmed what the women already thought: There was a genetic reason why almost every woman in the family has had cancer since the generation of Brown and Andrews' great-great-grandmother.
Smith got preventive prophylactic surgery in 2001 before she was tested genetically. Because she knew the risk of developing cancer was high, she had her breasts removed, then reconstructed.
"I was a ticking time bomb," Smith said. "Every woman in my family had it, and my grandmother had died at 33. I had three children to think about."
It's the same decision actress Angelina Jolie chose to make after she was tested for BRCA mutations. There are BRCA1 and BRCA2 mutations, which contribute to 5 to 10 percent of all breast cancer cases, according to the National Cancer Institute.
When Smith chose to get the surgery, it was virtually unheard of. Smith said she was the first case her insurance company had encountered about the preventive surgery.
Brown, who is married, wants to have a family before having the preventive surgeries done. Knowing about the gene has moved her timeline for having children up a bit, she said.
She knows from talking with genetic counselors there is a likelihood she could pass on the gene. There will be a talk with her children when the time comes to consider testing at 18, but Brown, a breast cancer awareness advocate, says she hopes there will be a cure by the time her children are adults.
Andrews is planning to get the surgeries in January.
"She decided to do it recently because, while she was visiting here, one of her friends had developed prostate cancer and began chemo," Brown said. "She decided she didn't want to go through that and made the decision to do it right away."
Insurance will cover some of it, and Andrews is planning on paying about $9,000 out-of-pocket, Brown said.
Brown wants her friends to be aware of cancer screening and the gene testing, but is mindful to not force her views on others.
"I know some people would rather not know," she said.
Smith got the genetic testing done after having a double mastectomy because, if she found out there was a high risk of developing breast cancer, the company could have considered it a pre-existing condition and not cover the surgery.
"It maybe just reaffirmed my decision," she said of the testing. "When I found out, I called my brother right away and called all my cousins and I told them that everybody needs to get tested for this."
Smith's brother, Dave Andrews, is the father of Brown and Amber Andrews. Smith's testing paved the way for the two sisters and their female cousin to get some answers genetically.
When Smith was tested, the test had to check for many indicators before finding the BRCA 1 mutation and cost thousands of dollars. Brown estimates the gene tests for her and her sister cost about $400 each because the gene to be tested was isolated.