Mammography and clinical breast examination are the two major techniques used to screen for breast cancer

Mammography and clinical breast examination are the two major techniques used to screen for breast cancer. However, as true for any screening test, they are not completely accurate. If it is determined, based on mammographic findings, that there is a possibility of breast cancer, this is usually confirmed or disconfirmed by a subsequent biopsy. A false positive test is a mammogram positive test that is disconfirmed by biopsy. The data in Table 1 were reported in a paper concerning breast cancer screening (Elmore, et al, New England Journal of Medicine 1998; 338(16): 1089-1096). Table 1 False positive breast cancer screening tests over a 10-year period # Screening tests 9762 # False positive tests 631 1. Another aspect of mammographic screening is the presence of false negatives. A false negative is a screen negative woman who has breast cancer. False negatives usually occur because the tumors are small and hard to detect. It is estimated that among women with breast cancer, 2% of all screening tests are false negatives. Suppose that there are 100 women who have breast cancer. What is the probability that at least 3 of them will not be detected by a mammogram?