Can women reduce the risk of breast cancer if her relatives have it?
The good news is the vast majority of women will not develop breast cancer in their lifetime - 88% based on data from the National Cancer Institute. But some face a higher risk than others, including women with one or more first degree relatives (mothers, daughters, and sisters) who have developed the disease.
Breast cancer develops from mutations in cancer-associated genes, and a few of those gene mutations are associated with a family history of breast cancer. Can anything be done to reduce that risk?
A major meta-analysis (a study pooling data from multiple studies) by the Collaborative Group on Hormonal Factors in Breast Cancer set out to quantify the increase in risk when one or more first degree relatives have been diagnosed with breast cancer and determine what factors, if any, can influence that risk. It turns out, among women with one or more first degree relatives with breast cancer, the risks vary by several factors, and some are controllable.
Number of Affected First-degree Relatives
The risk of developing breast cancer is 80% higher (22%) for women with one affected relative compared to women with no affected relatives (12%). When a woman has two first-degree relatives with breast cancer, the risk is 193% higher (36%). For women with three affected relatives, the risk is 290% higher (47%). However, the sample size for this last group was small, and the actual risk could be as low as that for women with two affected relatives-- or as high as 649% higher.
Relative's Age at Diagnosis
The younger the first-degree relative's age at diagnosis, the higher the risk a woman will develop breast cancer. For example, if the first-degree relative was under 40 when diagnosed with breast cancer, the risk a woman under 40 will develop breast cancer is 5.7 times higher than a woman with no first degree relatives with breast cancer. This risk factor declines with the relative's age at diagnosis and the age of the woman.
Children
Having children when under age 30 reduces the risk of breast cancer for a woman one or more first-degree relatives with breast cancer. The risk reduction is 22% (having a first child when under 20) to 28% (having a first child when under 30. Having two or more children can also decrease the risk - by 20% for two children, by 26% for three and 44% for four or more.
Use of Oral Contraceptives
Women with one or more first degree relatives with breast cancer who had used oral contraceptives within the past ten years had a 23% lower risk than those who had never used oral contraceptives or who last used them 10 or more years ago. However, use of oral contraceptives by women 35 and older creates its own set of risk factors.
Use of Hormone Replacement Therapy
The use of hormone replacement therapy increases the risk a women with one or more first degree relatives with breast cancer will develop it herself. It doesn't matter whether the woman last used hormone replacement therapy more than five years ago or within the past five years - the risk of developing breast cancer is 18% to 20% higher than women who never used hormone replacement therapy.
Weight
Women under 50 with one or more first-degree relatives with breast cancer increase their risk even more if they are overweight or obese (have a body-mass index greater than 25). The risk of developing breast cancer increases by an additional 20%. This risk factor diminishes with age so over-weight or obese women over 50 with one or more affected first degree relatives do not face any higher risk than that associated with the family history.
How Can a Woman with First-degree Relatives with Breast Cancer Reduce Her Risk?
For women with first-degree relatives with breast cancer, many of the factors affecting their breast cancer risk are not controllable - age, number of relatives with breast cancer, age at onset of menopause - some are partially or totally controllable. A woman can try to have her first child before the age of 30, maintain a normal weight, avoid hormone replacement therapy and avoid behaviors associated with higher risk of breast cancer in general, such as smoking and heavy alcohol consumption.
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