Understanding Your True Risk of Breast Cancer
Are you frightened, even worried, when you hear the statistics about breast cancer risk? For most women her greatest cancer fear is breast cancer. But how many women actually understand her true risk of breast cancer?
This week I talked with Patricia T. Kelly, Ph.D., a medical geneticist who specializes in cancer risk assessment and counseling. We discussed hormone replacement therapy, hereditary factors, benign breast disease, the real meaning of statistics, genetic testing, and other issues that can affect personal breast cancer risk.
Dr. Kelly is the author of several books, including her most recent "Assess Your True Risk of Breast Cancer." It seems a constant occurrence that new statistics and studies reveal an increased or decreased risk of breast cancer. These numbers are often confusing, and leave many of us wondering if we are doing the right thing. A respected expert in her field, Dr. Kelly provides answers that clear up much of this confusion. You might be surprised to discover your risk of developing breast cancer is actually lower than you thought!
Q. Why is the 1 in 9 statistic about breast cancer risk in women misleading?
A. Risk information without a time frame is rarely useful and can often be misleading. For example, a ten percent risk today is very different from a ten percent risk spread over the next ten years.
The average woman's breast cancer risk of 1 in 9 (or 11 percent) is actually a woman's risk from age 20 to age 80. The risk from 20 to 50 is 2 percent, with 9 percent of the risk after age 50. When a woman with the average risk reaches age 50 without a breast cancer diagnosis, 2 percent of her risk is gone.
Q. What is the real risk of breast cancer for women with both a mother and sister who have had breast cancer?
A. Less than 10 percent of all breast cancer is thought to be due to strong hereditary factors. Therefore, in a group of women whose mothers have breast cancer, some of the mothers' breast cancers are likely to be due to strong hereditary factors, but most will be nonhereditary. If you calculate the overall risk to all daughters in this mixed group it will be too low for the few whose mother's breast cancer is due to strong hereditary factors and too high for most of the women whose mother's breast cancer is not hereditary. Each woman whose mother has breast cancer therefore is likely to benefit by having her risk assessed in an individual manner.
Q. Do women face a hereditary risk of breast cancer from the male side of their family or is the hereditary risk only from the female side?
A. An increased hereditary risk of breast cancer (and ovarian cancer) can be passed through the father's side of the family as well as the mother's. In some families the same genetic change (mutation) that increases breast cancer risk also increases the risk of ovarian cancer.
Q. How does hormone replacement therapy in menopause affect breast cancer risk?
A. Studies of hormone replacement therapy at menopause compare breast cancer risk to a group of women who took hormones with a group of women who did not. Many risk factors for breast cancer are unknown, so it is difficult to construct studies in which the two groups are the same except for taking hormones. For this reason, statisticians point out that when the difference in risk between two groups is less than three-fold (a relative risk or odds ratio 3 or greater), other differences between the groups, and not hormones, are more likely to be the cause of the difference in risk.
Most studies of women who take hormone replacement therapy at menopause either find no increase in breast cancer risk or find one that is far smaller than a three-fold increase. The often cited study of nurses, for example, found a 1.5 fold increase in breast cancer risk to one group of hormone users and no increase in risk to another group of hormone users when compared to a group of women who never used hormones. Both groups had used hormones for ten years, but the group with the higher breast cancer rate had more mammograms. In this study, therefore, the greater use of mammography may have contributed to finding more breast cancers in the group that had a higher risk.
Risks presented as comparisons, such as 1.5 times greater, are generally less useful than when the same information is presented as an actual risk without comparing risk in one group to that in another. For example, even if one assumes that hormone replacement therapy increases breast cancer risk by 30 percent to 50 percent (1.3 to 1.5 in comparison terms) this would be an additional three breast cancers in 1,000 women over the course of ten years!
Studies on hormone replacement therapy at menopause either show no increase in breast cancer risk to women in general, to women with a family history of breast cancer, or to women with benign breast disease, or show a very small increase in risk that might be due to differences between groups of women who do and do not take hormones.
Next page>Benign breast disease, ductal carcinoma, tamoxifen, genetic testing, other influences Page 1, 2
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