TABLE 4-1 Age-Specific Probabilities of Developing Breast Cancer1

If current age is

Then the probability of developing breast cancer in the next 10 years is:

or 1 in:

20

0.05%

2,152

30

0.40%

251

40

1.45%

69

50

2.78%

36

60

3.81%

26

70

4.31%

23

BOX 4-2
Epidemiological Methods for Discovering Genetic Links to Disease

Case-control studies are retrospective observational studies in which investigators identify one group of patients with a specified outcome (cases) and another group without the specified outcome (controls). Investigators then compare the histories of the cases and the controls to determine the extent to which each had the possible risk factor being investigated.

Cohort studies are observational studies in which outcomes in a group of patients who possess the possible risk factor being tested (the cohort) are compared with outcomes in a control group of patients who do not possess the possible risk factor. For example, the occurrence of breast cancer would be compared between two groups of women neither of whom have breast cancer at the beginning of the study; one of the groups would possess the possible risk factor and the other group would not. The number of new cases of breast cancer in the two groups would be compared over time.

Approximately 70 percent of women who develop breast cancer have the type of cancer called hormone receptor positive, which means that the cancerous tissue contains receptors for estrogen and/or progesterone. This association may, therefore, prove to be more relevant among women with elevated levels of these hormones, for example, premenopausal women or women using hormone replacement therapy.17,40,46 More research into risk profiles of such subtypes of breast cancers may elucidate a clearer connection between risk factors and the development of breast cancers. Although many factors that influence risk have been identified, it is still not possible to determine which women will develop breast cancer and which will not.



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