National Academies Press: OpenBook

Clinical Practice Guidelines: Directions for a New Program (1990)

Chapter: Efficacy of Screening Tests

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Suggested Citation:"Efficacy of Screening Tests." Institute of Medicine. 1990. Clinical Practice Guidelines: Directions for a New Program. Washington, DC: The National Academies Press. doi: 10.17226/1626.
Page 131
Suggested Citation:"Efficacy of Screening Tests." Institute of Medicine. 1990. Clinical Practice Guidelines: Directions for a New Program. Washington, DC: The National Academies Press. doi: 10.17226/1626.
Page 132

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APPENDIX B 131 age 30 to 180 per 100,000 at age 50.3 The risk for women with a family history of premenopausally diagnosed breast cancer in a first-degree relative is about two to three times that of the average woman of the same age in the general population.3,4,5 Women with previous breast cancer are at increased risk, as are women with a history of benign breast disease.3,4,5 Other factors with some clinical or statistical association with breast cancer include first pregnancy after age 30, menarche before age 12, menopause after age 50, obesity, high socioeconomic status, and a history of ovarian or endometrial cancer.3,4,5 Efficacy of Screening Tests The three screening tests usually considered for breast cancer are clinical examination of the breast, x-ray mammography, and breast self-examination (BSE). The sensitivity and specificity of clinical examination of the breast varies with the skill and experience of the examiner and with the characteristics of the individual breast being examined. Over the five years of the Breast Cancer Detection Demonstration Project (BCDDP), the estimated sensitivity of clinical examination alone was 45%.8 Data from studies using manufactured breast models show that mean sensitivity among registered nurses was 65% compared with 55% for untrained women.8,9 Detection by physicians was 87% for lumps 1.0 cm in diameter, a size comparable to that used in the studies involving nurses and women.8,10 Estimates of the sensitivity of mammography depend on a number of factors, including the size of the lesion, the age of the patient, and the extent of follow-up to determine the proportion of ''negative" masses that are later found to be malignant (i.e., false negatives). The average sensitivity of the combined clinical examination and mammography in the five years of the BCDDP was 75%. The estimated sensitivity for mammography alone was 71%.8 A recent report from a multicenter trial estimated the sensitivity of an initial mammographic examination to be about 75%.11 In a study of 499 women, mammography had an overall sensitivity of 78%, but it was reduced to 70% when only lesions under 1.0 cm in diameter were considered.12 Sensitivity for all breast cancers in women over 50 was 87%, while sensitivity in women under 51 was 56%. In the 10-year follow-up of a Dutch study, the sensitivity of mammography was 80% for women aged 50 and above and 60% for those under 50.13 The specificity of mammography is about 94-99%.11,13 Even with this excellent specificity, however, false positives can occur frequently if the test is performed routinely in populations with a low prevalence of breast

APPENDIX B 132 cancer. Thus, most abnormal results of mammograms performed on young women without known risk factors for breast cancer are likely to be false positives. BCDDP data show that only 10% of women with positive (mammography and clinical examination) screening results were found to have cancer,14 and a recent multicenter trial reported a positive predictive value of only 7% for initial mammographic examinations. 11 There is no study that shows that the sensitivity or specificity of mammography is increased when "baseline" mammograms are available for comparison. Studies of mammography have shown large variations in observer (radiologist interpreter) performance.15,16,17 In a study using 100 xeroradiographic mammograms, including 10 of women with proven cancers, the number of lesions identified as "suspicious for cancer" by 9 radiologists ranged from 10 to 45.15 In a large breast cancer screening study in Canada, agreement was poor between radiologists at five screening centers and a single reference radiologist.16 Because exposure to ionizing radiation can be carcinogenic, widespread testing by mammography has the potential of producing some cases of radiation-induced cancer. However, radiation exposure from mammography has decreased dramatically with the development of dedicated mammography equipment and low- dose techniques.18,19 Radiation exposure varies with breast size as well as with the specific equipment and technique used.17,18,19 Thus, it is important for operators to use low-dose equipment and proper technique to limit unnecessary exposure to ionizing radiation during mammography. Self-examination of the breast appears to be a less sensitive form of screening than clinical examination, and its specificity remains uncertain. Using reasonable assumptions applied to data from the BCDDP, the estimated overall sensitivity of BSE alone was found to be 26% in women also screened by mammography and physical examination. 8 Estimated BSE sensitivity in the BCDDP varied by age group; it was most sensitive for women 35-39 years of age (41%) and least sensitive for women aged 60-74 (21%).8 Among participants in a breast cancer registry, BSE was reported to detect 34% of cancers.8,20 In a study of women's ability to detect breast lumps, untrained volunteers were able to detect 25% of lumps ranging in size from 0.25 to 3.0 cm in diameter.8,21 The study showed that the sensitivity of BSE can be improved by training. A 30-minute training session increased the mean lump detection rate to 50%.21 Although training sessions have increased detection rates, they also increase false-positive rates. False- positive BSE may result in unnecessary physician visits, heightened anxiety levels in women, and increased radiographic and surgical procedures. No study yet reported has directly compared the sensitivity or specificity of self-

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