Among U.S. women, breast cancer is the most commonly diagnosed form of cancer (other than skin cancer) and is second only to lung cancer as a cause of cancer-related death. Approximately 192,000 new cases of breast cancer were diagnosed and 40,200U.S. women died of breast cancer in 2001. Rates increase markedly with age (after age 40). Additional risk factors include: family history of breast cancer; genetic factors; particular breast changes; estrogen exposure (early menstruation, late menopause, hormone replacement therapy; and late childbearing). Mammography is a radiographic screening test widely recommended for early detection of breast cancer. Other early detection methods include breast self-exam (BSE) and clinical breast examination (CBE); existing research is insufficient to determine the effectiveness of these methods. (Reference: USPSTF, 2002)Question 1a: (4 points)One million (1,000,000) U.S. women, aged 60-79 years, are screened for breast cancer using mammography. Assume that the test has a sensitivity of 85% and a specificity of 96%, and that the true prevalence of undiagnosed breast cancer* among these women is 430/100,000. Construct a 2x2 table to show the distribution of screening results for this population. Fill in all cells of the table. Mammography Screening Exam With Breast Cancer Without Breast Cancer Total Positive Negative Total Question 1b (2 points)Calculate the predictive value positive (PV+) and the predictive value negative (PV-)of the mammogram screening test.PV+ =PV- =*i.e. the population to be screened, which does not include those with previously diagnosed breast cancer. Prevalence here generally refer to cancers that will be diagnosed within 1 year after screening. Keep this in mind for all following questions.Question 2a (4 points)Assume that you are screening a population of 1,000,000 women, ages 60-79, all of whom have a family history of breast cancer. The sensitivity and specificity of mammography are the same as in Question 1, 85% and 96% respectively. The true prevalence of breast cancer in this population is 800/100,000. Construct the 2x2 table (fill in all of the cells). Mammography Screening Exam With Breast Cancer Without Breast Cancer Total Positive Negative Total Question 2b (2 points)Now calculate PV+ and PV-.PV+ =PV- =Question 2c (2 points)Why does the value of the PV+ change over that calculated in Question 1b?Question 3a (2 points)An asymptomatic 65 year-old woman with a family history of breast cancer (Question 2) has had a positive mammogram. Using the value for the PV+ that you calculated in Question 2b and using lay terms (that is, language that the average person can understand), please explain the results of this test to the patient.Question 3b (2 points)An asymptomatic 65 year-old woman with a family history of breast cancer has had a negative mammogram. Using the value for the PV- that you calculated in Question 2b and again in lay terms, please explain the results of this test to the patient.5Question 4 (2 points)From Questions 1 and 2 and your readings - if sensitivity and specificity remain constant, what is the relationship of prevalence:to the PV+?to the PV-?In reality, mammograms are quite difficult to read and interpret. Accuracy depends on a number of factors, including the size of the lesion, the density of a woman's breast tissue, the woman's age, the hormone status of the tumor, and the quality of the radiographic image. The radiologist's interpretive skill is another major factor in how accurately the mammogram is evaluated. In short, there is not a hard and fast cutoff point or criterion of positivity that distinguishes a positive mammogram from a negative mammogram. Rather, mammograms of women both with cancer and without cancer may show findings that may range from "not suspicious" to "highly suspicious".Even though the "cutoff" used in interpreting mammograms is according to each reader's judgement, the following example uses a hypothetical "cutoff level" to illustrate the impact of using different decision-making criteria to interpret mammograms. Figure 1 shows that the appearance of mammograms (in terms of how "suspicious" they appear) may be similar for women with and without breast cancer. All women to the right of (or above) whatever cut-off point is used will test positive. Thus, changes in interpretation criteria affect the accuracy of the screening results for women with breast cancer as well as women without breast cancer. This will be true for almost all types of screening tests - because for most conditions, the distributions of the underlying biological parameters for early detection of disease overlap. Thus, screening tests are generally imperfect predictors of disease status.Women without breast cancerFigure 1. Hypothetical distribution of "cut-off points" in mammogram results among women with and without breast cancer. All women to the right of the cut-off point will screen positive. Women to the left of the "cutoff will be screen negative.Women with breast cancer"A" "B" "C"Lowest - - - Cut-Off Points - - - HighestSay that a radiologist has been using a cut-off level of "A" (from Figure 1) for calling a mammogram positive. Subsequently, she begins to use a higher cut-off level, "B" for determining that a mammogram is positive.Question 5a (2 points)With the use of a higher cut-off level (B), does the mammogram's sensitivity increase or decrease? In lay terms, explain what this change in sensitivity means for any population, i.e. regardless of prevalence.Question 5b (2 points)Does the mammogram's specificity increase or decrease? In lay terms, explain what this change in specificity means for any population, i.e. regardless of prevalence.Question 6 (2 points)Considering the results from previous questions on this case study, what is the relationship between the sensitivity and the specificity of a screening test?Question 7 (4 points)Consider the positive and/or negative implications of changing the criteria for a positive mammogram for 4 separate issues (clinical, economic, psychological, etc.). Briefly describe how these considerations might be associated with using a higher cutoff level (as in Question 5a and 5b) for calling the mammogram positive. (List 4 separate issues; you will not get credit for pluses and minuses of the same issue. Relate them to this topic specifically)One area of scientific controversy involves breast cancer screening among women ages 40-49. Among these younger women, "the evidence that screening mammography reduces mortality from breast cancer is weaker, and the absolute benefit of mammography is smaller, than it is for older women." (USPSTF, 2002) Let's look at an example applied to this age group.Question 8a (4 points)One million U.S. women, aged 40-49 years, are screened for breast cancer using mammography. Assume that the test has a sensitivity of 70% and a specificity of 93%, and that the true prevalence of undiagnosed breast cancer among these women is 160/100,000. Construct a 2x2 table to show the distribution of screening results for this population. Mammography Screening Exam With Breast Cancer Without Breast Cancer Total Positive Negative Total Question 8b ( 2 points)Calculate the PV+ and the PV- of the mammogram screening test for women 40-49.PV+ =PV- =Question 8c (2points)Compare the PV+ value calculated here in Question 8b with the PV+ value calculated in Question 2b. Are they different? What factor(s) account for the differences in these values?Simultaneous or Parallel Screening TestsAnother concern of the above results is that mammography missed 30% of women with breast cancer (false negatives). One way to improve breast cancer screening may be to conduct clinical breast exams (CBE) at the same time as a woman is referred to screening mammography. There is good evidence that CBE detects some cancers that are missed by mammography. However, the specificity of CBE appears somewhat lower than that of mammography, and mammography plus CBE is associated with mortality reductions that are comparable to those using mammography alone (USPSTF). The USPSTF has evaluated the evidence for or against the routine use of CBE as "inadequate".Let's look at an example where CBE is used in parallel (simultaneously) with mammography for women 40-49 years old. In simultaneous screening, women who are positive for at least one test (mammography, CBE, or both) are called "positive" and are referred for further confirmatory testing. Conversely, women whose CBE andmammogram are both negative are considered to be "negative" on the overall screening. Here are some important definitions:Net sensitivity: the proportion (%) of women with breast cancer who are detected as positive by AT LEAST ONE of the two screening tests (either mammography, CBE, or both).Net specificity: the proportion (%) of women without breast cancer who are evaluated as negative by BOTH of the two screening tests (mammography and CBE)..An example of the net effect of parallel or simultaneous screening Using Clinical Breast Examinations (CBE) and mammographyOne million women, ages 40-49 (true prevalence of undiagnosed breast cancer /100,000), are given both a clinical breast exam and a mammogram. In this study, mammography has a sensitivity of 70% and a specificity of 93%.In addition, among those women with breast cancer whose cancers were missedby mammography (false-negatives), 50% were detected by CBE.Among those women without breast cancer whose mammograms were negative, 2% are labeled "positive" by CBE. (That is, 2% of the mammography total number of negatives have a positive CBE and are therefore "false positives".)Question 9a (4 points)Fill in the following 2x2 table for the combined results of mammography and CBE screening. Breast Cancer Screening Tests Breast Cancer Diagnosed Yes No Total One or both positive Both negative Total 1,000,000 Question 9b ( 2 points)What is the net sensitivity of this simultaneous screening program?Question 9c (2 points)What is the net specificity of this simultaneous screening program?Question 9d (2 points)What is the PV+ value for this simultaneous screening program?11Question 9e (2 points)Compare the PV+ value you calculated in Question 9d with the PV+ value you calculated in Question 8b. Are they different and if so, how do they differ? Since the populations screened were the same size, of the same age group (women 40-49 years of age) with the same breast cancer prevalence (160/105), if the calculated PV+ values are different, what factor would account for this difference?Question 9f (not graded-for discussion only)Compare the results of using single modality screening (mammography only) as was done in Question 8 with the results from the use of simultaneous screening (mammography and CBE) as was done in Question 9 on the same population with the same breast cancer prevalence. Consider the changes in net sensitivity and net specificity over single modality screening (mammography only) sensitivity and specificity. Is there a gain in one or the other and why? Is the extra cost of simultaneous screening justified? From a public health perspective, which one would you recommend for a low prevalence population and why.Question 10 (4 points)A large national Health Maintenance Organization (HMO) has asked you to serve on an expert panel. This panel has been asked to develop age-specific recommendations regarding routine breast cancer screening among the HMO's female members. List four specific issues that you will consider in developing these recommendations. You do not need to make any recommendations here, simply discuss the considerations that go into the process of making them. (Hint: Refer to principles of good public health screening programs from lecture or from the textbook, Chapter 16 - then apply the most relevant of these principles to this situation.)13REFERENCESScreening for Breast Cancer: Recommendations and Rationale. U. S. Preventive Services Task Force. Agency for Healthcare Research and Quality, Publication No. 03-507A, August 2002, pp. 171-179.What you need to know About Breast Cancer. National Cancer Institute. (www.cancer.gov/cancerinfo/wyntk/breast)
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