A very large research study done in Sweden found that the sisters of women diagnosed with breast cancer have a higher than average risk of breast cancer. This increased breast cancer risk lasts a lifetime.
These results are important because some doctors thought that a sister of a woman diagnosed with breast cancer was at higher risk only when she was about the age when her sister was diagnosed.
Though sisters of women diagnosed with breast cancer have a lifetime increased risk of disease, the researchers found that the amount of increased risk changed over time. Between ages 20 and 40, sisters of women diagnosed with breast cancer have a nearly 6.5 times higher than average risk of breast cancer. After age 50, this risk drops to about double the average risk of breast cancer. This pattern was the same no matter how old the first sister in the family was when diagnosed with breast cancer.
These results are credible because the researchers looked at medical information from more than 16,000 women diagnosed with breast cancer and almost 24,000 sisters of these women. The medical information included more than 40 years of health care records for these women. Sweden has a national health care system with standard ways of keeping medical records, which makes it possible to do research like this.
If you're a woman whose sister has been diagnosed with breast cancer (if you've been diagnosed, pass this on to your sisters), you might want to consider:
- Talking to your doctor about whether a breast cancer screening plan for high risk women risk makes sense for you. This might mean starting screening before the usual starting age of 40. The study reviewed here found that sisters had the highest risk when they were between ages 20 and 40. Your screening plan might include breast ultrasound and MRI, as well as mammograms.
- Sticking to your screening plan as you get older because your increased risk of breast cancer lasts a lifetime.
- Talking to your doctor about whether genetic testing for abnormal breast cancer genes makes sense based on your sister's history and other family medical history.
- Doing all that you can to keep your breast cancer risk as low as it can be. While you can't change your genes, you can make healthy diet, exercise, and lifestyle choices that can lower your risk.
To learn more about breast cancer risk and how you can keep your risk as low as it can be, visit the Breastcancer.org Lower Your Risk section.
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