About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child.
Genes are particles in cells, contained in chromosomes, and made of DNA (deoxyribonucleic acid). DNA contains the instructions for building proteins. And proteins control the structure and function of all the cells that make up your body.
Most inherited cases of breast cancer are associated with two abnormal genes; BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two).
Everyone has BRCA1 and BRCA2 genes. The function of the BRCA genes is to repair cell damage and keep breast cells growing normally. But when these genes contain abnormalities or mutations that are passed from generation to generation, the genes don’t function normally and breast cancer risk increases.
You’re much more likely to have an abnormal breast cancer gene if:
- You have blood relatives (grandmothers, mother, sisters, aunts) on either your mother’s or father’s side of the family who had breast cancer diagnosed before age 50.
- There is both breast and ovarian cancer in your family, particularly in a single person.
- There are other gland-related cancers in your family, such as pancreatic, colon, and thyroid cancer.
- Women in your family have had cancer in both breasts.
- You are of Ashkenazi Jewish (Eastern European) heritage.
- You are African American and have been diagnosed with breast cancer at age 35 or younger.
- A man in your family has been diagnosed with breast cancer.
The average woman in the United States has about a 1 in 8, or a 12-13%, risk of developing breast cancer in her lifetime. The risk for breast cancer in BRCA mutation carriers has been found to be at least 56% and in some families has been found to be as high as 87%.
A new study suggests that diagnostic tests that use radiation (mammograms and X-rays both use radiation) done before age 30 in young women with an abnormal BRCA1 or BRCA2 gene increases breast cancer risk even more.
The research was published online by the British Medical Journal on Sept. 6, 2012. Read the abstract of “Exposure to diagnostic radiation and risk of breast cancer among carriers of BRCA1/2 mutations: retrospective cohort study (GENE-RAD-RISK).”
The study, called GENE-RAD-RISK, looked at the radiation exposure of 1,993 women who had an abnormal BRCA1 or BRCA2 gene:
- 65% of the women had an abnormal BRCA1 gene
- 35% of the women had an abnormal BRCA2 gene
The women were from France, the United Kingdom, and the Netherlands.
About 43% of the women (848 of them) had been diagnosed with breast cancer.
The women filled out a detailed questionnaire on the number of diagnostic tests that used radiation they had, including:
- fluoroscopy (a continuous X-ray, kind of like an X-ray movie)
- X-rays of the chest or shoulders
- CT scans of the chest or shoulders
- bone scans of the chest or shoulders
About half the women had an X-ray at some point in their lives, with most having at least two before age 40. Most of the women also had at least two mammograms before age 40.
The researchers used a mathematical formula to figure out how much exposure to radiation affected the women’s risk of breast cancer.
They found that if a woman with an abnormal BRCA1 or BRCA2 gene had a diagnostic test that used radiation before she was 30 years old, her risk of breast cancer went up.
So, if all women with an abnormal BRCA1 or BRCA2 gene had one mammogram before they were 30, the number of women who were diagnosed with breast cancer by age 40 would go up from 9 out of 100 to 14 out of 100.
While the results of this study sound scary, it’s important to keep several things in mind:
- There are breast cancer screening tests that don’t use radiation, such as MRI (magnetic resonance imaging).
- Abnormal BRCA1 and BRCA2 genes are relatively rare. Most women don’t have a higher risk of breast cancer if they have diagnostic tests that use radiation.
- The women in this study had to remember how many diagnostic tests they had, some of which may have been done more than 15 years earlier; it’s likely that some of the women didn’t remember everything correctly.
- The researchers estimated the radiation doses the women received from the diagnostic tests; in some cases, these estimates may not be perfectly accurate.
- Because this study was done in Europe, where some countries used fluoroscopy to screen for tuberculosis, the results aren’t conclusive for women living in the United States.
- The benefits of X-ray diagnostic tests almost always outweigh any risks.
The American Cancer Society (ACS) recommends annual breast MRI screening for women with an abnormal BRCA1 or BRCA2 gene. The ACS also recommends that screening start at age 25 for women with an abnormal BRCA1 and BRCA2 gene, though when screening starts may be different for every woman, depending on how young the first person in the family was when diagnosed. Also, no professional organization recommends screening tests that use radiation before age 30 for women with an abnormal BRCA1 or BRCA2 gene.
If you know you have an abnormal BRCA1 or BRCA2 gene, you and your doctor will work together to create a breast cancer screening plan that makes the most sense for your particular situation. If your screening plan includes mammograms, you may want to talk to your doctor about this study and ask if annual MRI screening would be a good option for you.
For more information on mammograms, X-rays, MRIs and other tests to detect breast cancer, visit the Breastcancer.org Breast Cancer Tests: Screening, Diagnosis, and Monitoring pages.