Estimated breast cancer risks for women with BRCA1 mutations vary significantly depending on whether they are based on studies conducted in highly selected cancer genetics clinic-based BRCA1 families (risk estimates generally on the high end) or in studies focused on women with BRCA1 mutations drawn from the general population (risk estimates generally on the low end).? This is likely because women and families tend to come to attention in cancer genetics clinics due to particularly remarkable breast cancer family histories, which may ? in some cases ? be correlated with other genetic and environmental factors that influence risk in subtle ways.
To the extent that these more subtle factors may vary in different populations, it is possible that lifetime breast and/or ovarian cancer risks may vary in different groups or geographies.? Interestingly, a recent study suggested that breast cancer rates were different for women with BRCA1 mutations in Poland versus North America.? In fact, the women in Poland had an estimated 49% risk up to age 70 versus an estimated 72% risk for women in North America.? The differences in annual risks were particularly large amongst the 25-39 year-old age group in that study.
Now a group led by Dr. P?l M?ller of Oslo University Hospital (Dr. M?ller has contributed substantially to what we know about the impact of BRCA1 and BRCA2 in Norway) has performed a similar analysis of breast cancer risks for BRCA1 carriers in Norway, looked at how the risk varies with age, and then compared the results with the prior study of risks in Poland and North America.? The Norwegian BRCA1 carriers were from a cohort study of clinic patients from the Outpatient Cancer Genetics Clinic at the Oslo University Hospital.? The study was initiated in 1989 with patients being followed through the end of 2011.? In total, 675 BRCA1 carriers with no prior diagnosis of breast or ovarian cancer and no prior risk-reducing bilateral mastectomy were in the study.
Annual Breast Cancer Rates for Women with BRCA1 Mutations in Norway are Highest for Women Age 50-59
The average yearly breast cancer rate for the studied women was 2.0% with an estimated breast cancer risk to age 70 of 60.8%.? The decade from age 50 to 59 had the highest yearly rate of breast cancer diagnosis ? 3.1%.? However, due to the study size, it is important to keep in mind that the 95% confidence intervals for the estimates for these risk by age tended to overlap some.? Thus, a much larger study would be necessary to estimate these risks with more certainty.
Average yearly rate of new breast cancer diagnoses (carcinoma in situ not included) in Norwegian BRCA1 carriers:
- Age 25-39: 1.9% per year
- Age 40-49: 2.2% per year
- Age 50-59: 3.1% per year
- Age 60+: 1.1% per year
Breast Cancer Risks to Age 70 for BRCA1 Carriers Were Estimated to be Intermediate Between Previously Published Risks for Women from Poland and North America
The results of this study suggest that the risks of breast cancer for BRCA1 carriers to age 70 may be intermediate between those recently published for Poland and North America (Norway: 61%, Poland 55%, and North America 69%).
However, when comparing the age-specific incidence rates for the Norwegian women, these were more similar to those previously reported in Poland than to those previously reported in North America.? Notably, there seems to be a spike in risk in the North American BRCA1 carriers in the 25-39 age group.
Bottom Line Implications for BRCA1 and BRCA2 Carriers
1. This new research paper serves as a good reminder that site-specific cancer rates for BRCA1 (and BRCA2) carriers can vary with age.? This is an important thing to keep in mind and to discuss with your healthcare provider in the context of decision-making regarding optimal cancer risk-reduction and screening approaches for you.
2. It also serves as a good reminder that there can be differences in breast cancer rates for BRCA1 carriers by geographical region.? Researchers have much to do to better understand why this is, but a few possibilities include:
- Founder mutations present more frequently in certain geographies could be associated with different risk
- Different environmental influences on cancer risk
- Distinct approaches to cancer risk-reduction and surveillance may lead to more opportunity to identify cancers in certain geographies
Much more work will be necessary to fully sort all of this out.
3. It would be great if cohort studies like this could be initiated in additional countries and regions of the world, as it might help us learn about differences in risk with distinct mutations or mutation types in BRCA1 (and potentially BRCA2), and it might also present a great opportunity to learn more about environmental impacts on cancer risks for BRCA1 and BRCA2 carriers.
4. We will have a future post here on the BRCAscoop Blog re: potential explanations for the spike seen in North American breast cancer rates in the 25-39 age group.
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How We Know This:
M?ller P, M?hle L, Vab? A, et al.? Age-specific incidence rates for breast cancer in carriers of BRCA1 mutations from Norway.? Clinical Genetics 2012 (published online before print Feb 9 2012)
Lubinski J, Huzarski T, Byrski T, et al.? The risk of breast cancer in women with a BRCA1 mutation from North America and Poland.? International Journal of Cancer 2011 (published online before print Aug 10 2011)
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Matt Mealiffe, M.D. is a Clinical Cancer Geneticist with dual board certification in Clinical Genetics and Internal Medicine. He received his undergraduate degree at Stanford University, his M.D. at the Yale University School of Medicine, and did his residency and fellowship training at the University of Washington. Dr. Mealiffe writes at BRCAscoop.com to improve BRCA1/BRCA2 carriers? understanding of issues important to their health and wellness.
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Source: http://brcascoop.com/2012/blog/norway-breast-cancer-rates-for-brca1-carriers-can-vary-with-age/
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