Mastectomy 16gene.html (article) 16gene.html health/ /the-story-of-a- previvor.html (video) health/ /the-story-of-a- previvor.html 0/2/77 (New England Journal of Medicine) 0/2/77

New England Journal of Medicine Volume 340:77-84January 14, 1999Number 2 Efficacy of Bilateral Prophylactic Mastectomy in Women with a Family History of Breast Cancer Lynn C. Hartmann, M.D., Daniel J. Schaid, Ph.D., John E. Woods, M.D., Thomas P. Crotty, M.D., Jeffrey L. Myers, M.D., P.G. Arnold, M.D., Paul M. Petty, M.D., Thomas A. Sellers, Ph.D., Joanne L. Johnson, R.N., Shannon K. McDonnell, M.S., Marlene H. Frost, Ph.D., R.N., Robert B. Jenkins, M.D., Ph.D., Clive S. Grant, M.D., and Virginia V. Michels, M.D. ABSTRACT Background Options for women at high risk for breast cancer include surveillance, chemoprevention, and prophylactic mastectomy. The data on the outcomes for surveillance and prophylactic mastectomy are incomplete. Methods We conducted a retrospective study of all women with a family history of breast cancer who underwent bilateral prophylactic mastectomy at the Mayo Clinic between 1960 and The women were divided into two groups — high risk and moderate risk — on the basis of family history. A control study of the sisters of the high-risk probands and the Gail model were used to predict the number of breast cancers expected in these two groups in the absence of prophylactic mastectomy. Results We identified 639 women with a family history of breast cancer who had undergone bilateral prophylactic mastectomy: 214 at high risk and 425 at moderate risk. The median length of follow-up was 14 years. The median age at prophylactic mastectomy was 42 years. According to the Gail model, 37.4 breast cancers were expected in the moderate- risk group; 4 breast cancers occurred (reduction in risk, 89.5 percent; P<0.001). We compared the numbers of breast cancers among the 214 high-risk probands with the numbers among their 403 sisters who had not undergone prophylactic mastectomy. Of these sisters, 38.7 percent (156) had been given a diagnosis of breast cancer (115 cases were diagnosed before the respective proband's prophylactic mastectomy, 38 were diagnosed afterward, and the time of the diagnosis was unknown in 3 cases). By contrast, breast cancer was diagnosed in 1.4 percent (3 of 214) of the probands. Thus, prophylactic mastectomy was associated with a reduction in the incidence of breast cancer of at least 90 percent. Conclusions In women with a high risk of breast cancer on the basis of family history, prophylactic mastectomy can significantly reduce the incidence of breast cancer.

Problems with Prob Franklin’s Law Miscommunication of risk Clouded thinking

Tests Reality Test YesNo Yes Hit False positive No Miss Correct rejection

Bayes Rule

For symptom-free women aged 40 to 50 who participate in screening using mammography, the following information is available for this region. The probability that one of these women has breast cancer is 0.8%. If a woman has breast cancer, the probability is 90% that she will have a positive mammography test. If a woman does not have breast cancer, the probability is 7% that she will still have a positive mammography test. What is the probability that a woman with a positive test actually has breast cancer? For symptom-free women aged 40 to 50 who participate in screening using mammography, the following information is available for this region. Out of 1000 women 8 will have breast cancer. Of these 8 women, 7 will have a positive mammograms. Of the remaining 992 women, 70 will have a positive mammogram. What is the probability that a woman with a positive test actually has breast cancer?

The probability that a given person has disease A is 1%. If the person has disease A, then a particular test will be positive 95% of the time. If a person does not have disease A, then the test will be positive only 4% of the time. If a person has a positive test result, what are the odds, he actually has the disease? The probability that a given person is lying is 4%. If the person has lies, then a lie detector test will be positive 99% of the time. If a person does not lie, then the lie detector test will be positive only 10% of the time. If a lie detector indicates a person is lying, what are the odds, he is lying?

1000 Telling Truth Lying Positive Test Negative Test Positive Test Negative Test