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Calculating the Risk of Developing Breast Cancer

The American Cancer Society calculates the following odds that a woman will develop breast cancer

Age Period Risk of Breast Cancer
Birth to age 39y 0.48 % (1 in 209)
Age 40 to 59y 4.11%  (1 in 24)
Age 60 to 69y 3.82%  (1 in 26)
Age 70 and older 7.13 % (1 in 14)
Lifetime Risk 13.22 % (1 in 8)
The risk for a given individual is related to a number of factors and a more estimate of risk can be developed for a patient. The best risk calculator is from the NCI here and here;  and from Halls (detailed) other general risk calculators on the web: site#1   You should also review the NCI section on risk factors and genetics

Assessing the Risk of Breast Cancer (The New England Journal of Medicine -- February 24, 2000 -- Vol. 342, No. 8 )

How to Evaluate Breast-Cancer Risk

Average Risk

Understanding the average risk of breast cancer provides a necessary context for individual risk assessments. The average lifetime risk of breast cancer in the U.S. female population at birth is 12 percent, or approximately one in eight.The longer a woman lives without cancer, the lower is her risk of breast cancer over the remainder of her lifetime. Thus, a 50-year-old woman who has not had breast cancer has an 11 percent chance of having breast cancer in her lifetime, and a 70-year-old woman who has not had breast cancer has a 7 percent chance of having breast cancer in her lifetime.

Epidemiological Risk Factors

Many studies have evaluated risk factors for breast cancer. Several factors have been consistently associated with an increased risk (see below) However, because many of these risk factors may interact, evaluating the risk conferred by combinations of risk factors is challenging. Other risk factors have been less consistently associated with breast cancer (such as diet, use of oral contraceptives, lactation, and abortion) or are rare in the general population (such as radiation exposure), and are not included in currently used prediction models.

Risk Factor Relative Risk
Age (50 or less vs > 50y) 6.5
Fam History (1st degree relative) 1.4 - 13.6
Second-degree relative 1.5 - 1.8
Age at Menarche (<12 vs 14+) 1.2 - 1.5
Age at Menopause (55+ vs < 55y)) 1.5 - 2.0
Age at first birth (>30 vs <20y) 1.3 - 2.2
Any Breast Biopsy 1.5 - 1.8
Biopsy = atypical hyperplasia 4.0 - 4.4
Hormone replacement 1.0 - 1.5

Risk-Prediction Models

The most commonly used model was developed by Gail et al. from the Breast Cancer Detection Demonstration Project, a large mammographic-screening program conducted in the 1970s. This model incorporates the number of first-degree relatives with breast cancer (0, 1, or greater than or equal to 2), age at menarche (<12, 12 to 13, or greater than or equal to 14 years), age at first live birth (<20, 20 to 24, 25 to 29 or nulliparous, or greater than or equal to 30 years), and the number of breast biopsies (0, 1, or greater than or equal to 2). It predicts the cumulative risk of breast cancer according to decade up to the age of 90 years. To determine eligibility for trial entry, the Breast Cancer Prevention Trial used a revised Gail model that also incorporates race, presence of atypical hyperplasia on breast biopsy, and 1987 population rates of breast cancer and death from other causes.

To calculate breast-cancer risk with the Gail model, a woman's risk factors are translated into an overall risk score by multiplying her relative risks from several categories (age at menarche, number of breast biopsies, family history, and age at first live birth) see below. This risk score is then multiplied by an adjusted population risk of breast cancer to determine the individual risk of breast cancer. The three categories are noted below:

Category A - Age at Menarche
Age at Menarche Relative Risk
14y or older 1
12 - 13y 1.10
under 12y 1.21

Category B - Age and Breast Biopsies
Number of Biopsies Age Relative Risk
0 any age 1
1 under 50y 1.70
1 50 or older 1.27
2 or more under 50y 2.88
2 or more 50 or older 1.62

Category C - Family History and Age at First Live Birth
1st Degree Relatives Age at 1st Live Birth Relative Risk
0 under 20y 1
0 20 - 24y 1.24
0 25-29y or nullip 1.55
0 30 or older 1.93
1 under 20y 2.61
1 20 - 24y 2.68
1 25 - 29 or nullip 2.76
1 30 or older 2.83
2 or more under 20y 6.8
2 or more 20 -24y 5.78
2 or more 25 - 29 or nullip 4.91
2 or more 30 or older 4.17

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