Roughly one in eight women faces breast cancer at some point in her life and nearly everyone has a mother, sister or friend who’s been diagnosed with it. These statistics are staggering and really demonstrate that breast cancer touches everyone.
As a genetics company, 23andMe is invested in understanding how genetics influences the development of cancer and how people respond to treatment (see bottom of post). But we’re motivated most of all by the stories we hear from people whose lives are impacted by the diseases we study. Below are two stories from women affected by breast cancer.
Jill’s 23andMe results came back in 2010 reporting a mutation in the BRCA1 gene, which can significantly raise a person’s lifetime odds of developing breast cancer. She and her husband then met with a genetic counselor and had the test redone by another genetic testing company only to get the same result.
This knowledge combined with her family history of cancer prompted Jill to meet with specialists and see what could be done to avoid developing the disease. Jill elected to have a double mastectomy, which decreases the odds of developing breast cancer. Said Jill, “the decision to have the double mastectomy, although it was scary, was actually pretty easy to make…Once I found out I was BRCA positive I felt I was in a lucky position to fight cancer before I ever got cancer.”
Roughly five to 10 percent of breast cancer cases occur in women with a genetic predisposition for the disease. Mutations in either the BRCA1 or BRCA2 genes account for most but not all inherited breast cancers in women and based on recent literature are associated with a lifetime risk of about 50-60% (previous estimates were around 80%). Genetic variation in other genes — for instance PTEN, TP53 and CHEK2 — has also been associated with breast cancer risk.
Joy is a breast cancer survivor who also lost both her mother and a sister to breast cancer. In order to find out if she had passed a genetic risk for the disease to her children she purchased 23andMe’s Personal Genome Service. She also paid the more than $3,000 it costs for complete BRCA screening. “I was two or three months into treatment and I figured I must be carrying the (variant),” Joy said.
It turned out that neither test pulled up a mutation in either the BRCA1 or BRCA2 genes. Although BRCA mutations account for most but not all inherited breast cancers in women, they still only explain a small fraction of total breast cancer cases. Non-genetic factors and mutations in other genes can also influence risk (see sidebar for more information). Still, for Joy, it was a relief to know that she isn’t passing one of the BRCA mutations to her children. “It was a revelation in that I assumed I had the (variant),” she said.