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Table 3. Power to detect differences in risk due to environmental effects in the prospective study as a function of follow-up time, exposure frequency and risk ratio of the exposure. The total number of cancer cases is assumed to be those given in table 1 above assuming 2000 females enrolled, 2/3 of which are unaffected at time of enrollment, a 30% rate of prophylactic mastectomy and a 50% rate of oophorectomy.

From: The International BRCA1 /2Carrier Cohort Study: Purpose, Rationale, and Study Design

  

Breast Cancer

Ovarian Cancer

Risk Ratio

Exposure Frequency

5 yrs

10 yrs

5 yrs

10 yrs

2

0.1

0.64

0.87

Not done

Not done

 

0.3

0.80

0.98

Not done

Not done

3

0.1

0.95

1.00

0.48

0.68

 

0.3

0.98

1.00

0.56

0.82

5

0.1

1.00

1.00

0.76

0.93

 

0.3

1.00

1.00

0.81

0.97