Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests Review of the National Cancer Institute Report and Public Health Implications (1999) / Chapter Skim
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4 Implications for Clinical Practice and Public Health Policy
4 Implications for Clinical Practice and Public Health Policy
Pages 86-124
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From page 86... ...
In either case, a screening program has value only when earlier detection of a disease results in earlier treatment that improves outcomes for the screened population. The appeal of screening as a means of reducing the burden of disease is powerful, and much has been claimed for a large array of tests that screen for iPrimary prevention aims to eliminate or reduce health threats (e.g., by treating waste water)
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From page 87... ...
recommended routine breast cancer screening for this age group (Taubes 1997) even though many scientists think that evidence is still inadequate to support general screening in this age group.
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From page 88... ...
Criteria for Clinical Recommendations In developing guidelines for thyroid cancer screening for people potentially exposed to I-131 fallout from the Nevada tests, the IOM committee began with several broad principles. Consistent with the established and recognized mission of the IOM and the National Research Council, the guidelines would be based on careful review and assessment of the scientific evidence.
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From page 89... ...
The committee's criteria for making recommendations about thyroid cancer screening for those exposed to I-13 1 from the Nevada tests can be depicted as an evidence pyramid (Figure 4.1~. The lowest tier involves evidence of a population health problem; next are the availability of effective treatment for the disease and of accurate and feasible screening tests; a yet higher tier involves evidence that early detection through screening improves outcomes; and at the top of the pyramid is evidence that benefits exceed harms.
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From page 90... ...
A committee recommendation about an intensive public health program to encourage or pay for screening would have to note (as described above) that the committee did not analyze the cost-effectiveness of thyroid cancer screening compared with other screening strategies of demonstrated value.
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From page 91... ...
Survival rates for this disease are high. The 10-year cancer-specific survival rate for persons with papillary carcinoma, the form linked to radiation exposure, is estimated at 95 percent and the 30-year survival rate is estimated at 90 percent (Wang and Crapo 1997; Mazzaferri and Jhiang 1994~.
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From page 92... ...
If a thyroid cancer, other than a very small one is found, surgery is often followed by radiation treatment with I-131 to destroy remnant thyroid tissue. After total or near-total thyroidectomy, patients require lifetime thyroid hormone replacement therapy, which if properly prescribed and monitored, does not present significant risk of adverse side effects.
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From page 93... ...
This clarification should, in turn, clarify whether it is warranted for DHHS to examine the evidence on screening for nonmalignant disease.5 THYROID CANCER SCREENING AND DIAGNOSTIC OPTIONS screening for thyroid cancer may involve two steps. For the first step, screening for thyroid nodules, the options reviewed by the committee are physical pal 5 As this report was nearing public release and after the committee had concluded its deliberations, the American College of Physicians published new recommendations for screening for benign thyroid disease (Helfand and others 1998; Helfand and Redfern 1998)
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From page 94... ...
The size and firmness of nearby lymph nodes are also checked by palpation. For asymptomatic, average-risk people, routine screening for thyroid cancer through palpation or ultrasound examination of the thyroid gland is not recommended (USPSTF 1996~.
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From page 95... ...
ACCURACY OF SCREENING AND FOLLOW-UP TESTS Palpation and ultrasound examinations are widely accepted as safe, low-risk procedures (Gharib 1997; Mazzaferri 1993a; Ashcraft and Van Herle 1981~. Concern about their use is not related to the direct risk of the procedures themselves but to their relative inaccuracy, particularly the probability of their producing false-positive results or identifying many very small nodules and cancers that are
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From page 96... ...
is low, even in most populations exposed to iodine-131, the great majority of positive test results for nodules will be false-positive test results for cancer when the nodule is biopsied. A detailed review of evidence about the accuracy of palpation and ultrasound in detecting thyroid nodules and of FNA in detecting thyroid cancer is presented in the "Screening for Thyroid Cancer" background paper (Appendix F)
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From page 97... ...
Those whose screening results are negative (no disease detected) may feel comforted, particularly if they view themselves as being at special risk of the disease.7 Even 7For breast cancer screening, Ransohoff and Harris (1997)
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From page 98... ...
This research also suggests that people may be unaware that screening may identify many cancers that will not progress even without treatment and that people want to be informed and to factor this information into their decisionmaking process. Evidence of Benefits from Early Detection through Thyroid Cancer Screening A major difficulty faced by the committee in considering its recommendations on screening for thyroid cancer was the absence of sound clinical research evaluating whether early detection of the disease through screening of asymptomatic people provides benefits in the form of longer life, reduced morbidity, or improved quality of life and whether such benefits outweigh any harms generated by screening.
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From page 99... ...
These same characteristics along with the relative inaccuracy of the screening tests make it unlikely that screening an asymptomatic population could improve already high survival rates. Screening test inaccuracy does, however, mean that a screening policy would produce many false-positive results (detection of noncancerous nodules)
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From page 100... ...
Table 4.1 summarizes the committee's assessment of probabilities relevant to a screening program based on palpation and some of the consequences of such a program. It does not include probabilities or effects for thyroid cancer mortality and morbidity for lack of supporting data.
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From page 101... ...
Sensitivity for cancer False positive rate including indeterminate and unsatisfactory samples with no cancer Complications of total thyroidectomy Recurrent laryngeal nerve injury Hypoparathyroidism Summary: Events per 10,000 patients screened Diagnosed to have nodules (true positives) Falsely diagnosed to have nodule (false positive)
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From page 102... ...
suggest that the way mammography screening for breast cancer in younger women has been debated may reflect how numerical information is framed and perceived. For example, advocates for screening might describe 16-18 percent reductions in relative risk for death, whereas skeptics might refer to 1-2 fewer deaths per 1,000 women who have been screened annually for 10 years.
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From page 103... ...
The choice of whether the benefits outweigh the harms is a personal, subjective judgment about the relative importance of potential outcomes based on individual preferences, life plans, and priorities. For example, when carefully informed about the probabilities and nature of outcomes of different clinical management strategies for localized prostate cancer, some patients will prefer not to undergo surgery, which carries some risk of incontinence or impotence; others faced with the same information will prefer surgery (Flood and others 1996; Beck and others 1994; Litwin 1994~.8 The ways of considering patient preferences and involving patients in decisionmaking range from what might be generally characterized as, simply, good communication to formal shared decisionmaking.
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From page 104... ...
Citing the lack of evidence, the Canadian Task Force on the Periodic 9The committee did not consider research protocols to constitute screening recommendations. For example, in research to investigate the effects of radioactive releases from the Hanford Nuclear Facility, protocols for examining exposed individuals for thyroid nodules and other conditions have been developed for the Hanford Thyroid Diseases Study (www.fhcrc.org/science/phs/htds)
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From page 105... ...
It does not cite scientific evidence of efficacy or effectiveness. The most direct recommendation for thyroid cancer screening in persons exposed to I-131 has been proposed (under the label "medical monitoring")
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From page 106... ...
COMMITTEE FINDINGS AND RECOMMENDATIONS Findings When evaluated against the criteria for screening recommendations set forth earlier in this chapter, the evidence reviewed by the committee does not support a clinical recommendation for routine screening for thyroid cancer in asymptomatic persons exposed to radioactive iodine from nuclear weapons testing at the Nevada Test Site. First, thyroid cancer is rare in the general population.
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From page 107... ...
Recommendations Public Health and Clinical Policies The committee recommends against public programs and clinical policies to promote or encourage routine screening for thyroid cancer in asymptomatic people possibly exposed to radioactive iodine from fallout as a consequence of the nuclear tests in Nevada during the 1950s. The lack of evidence that early detection of thyroid cancer through routine screening of asymptomatic persons improves health precludes a positive recommendation to screen people routinely for a disease characterized by slow progression, high survival rates without screening, and high rates of false-positive test results that can lead to unnecessary surgery and other harms, including some,
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From page 108... ...
Although the committee recommends against policies that encourage or promote routine screening, it is essential that clinicians respond sensitively and constructively to concerned patients who come to them seeking advice. Such a response will involve listening to the patients' concerns; discussing their possible exposure to iodine-131 and other risk factors for thyroid cancer; explaining that thyroid cancer is uncommon even in people with some exposure to I-131 and that the thyroid cancer linked to I-131 exposure is rarely life threatening; describing the process, benefits, and harms of screening and the lack of evidence showing that people are better off with it than without it; checking patient understanding of the information presented; and jointly deciding how to proceed.
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From page 109... ...
(If ATSDR proceeds with its medical monitoring program, it might nonetheless consider testing more and less formal ways of discussing benefits and harms with patients and reaching decisions about screening.) In addition to these practical considerations, a number of committee members also believed that formal shared decisionmaking is most appropriate for certain kinds of "close call" situations as explained above and that thyroid cancer screening does not qualify as such a situation.
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From page 110... ...
Patient and Public Information Although screening programs whether or not they are supported by scientific evidence can be a popular response to con
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From page 111... ...
Others with relevant experience in communicating about radiation risk include the Centers for Disease Control and Prevention, the Hanford Health Information Network, and the Hanford Thyroid Disease Study. Although managed care organizations are unlikely to have much experience with communicating about radiation risk, organizations such as Group Health Cooperative and Stanford's Center for Patient Preferences may have useful insights about developing effective public information about screening tests.
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From page 113... ...
97-4264, 1997) , the Institute of Medicine/National Research Council report "Exposure of the American People to Iodine-131 From Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications," and several Web pages at the National Cancer Institute site (http://rex.nci.nih.gov)
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From page 114... ...
· Thyroid cancer is rarely life-threatening; 30-year survival is over 90 percent for papillary thyroid cancer, the form linked to radiation exposure. · Accurately identifying people's past exposure to I- 1 31 is usually not possible because necessary data on the key risk factors from four decades ago are generally not available or are unreliable.
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From page 115... ...
and others with expertise in public health and evidence-based medicine found that there is insufficient evidence to recommend routine screening for thyroid cancer or other thyroid disease in people who are asymptomatic, whether or not they have been exposed to I-131. For physicians who see patients concerned about thyroid cancer and interested in screening, a process of shared decisionmaking is appropriate.
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From page 116... ...
You can then explain that the primary screening test is palpation, which looks for thyroid nodules using a physical examination of the neck, combined with questions about possible symptoms (e.g., hoarseness) and risk factors (e.g., radiation therapy at a young age)
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From page 117... ...
Although the program might contribute to knowledge in this area, the ATSDR medical-monitoring program is not likely to produce useful information about mortality effects of screening for thyroid cancer because the population that requests screening and meets eligibility criteria will be self-selected and because high long-term survival rates can be expected without screening. The committee already has noted that the results of the Hanford Thyroid Disease Study (which is a research effort rather than a screening program)
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From page 118... ...
concluded that the evidence did not support a positive recommendation for a program to promote systematic thyroid cancer screening for those potentially exposed to I-131 from the Nevada atomic bomb testing program; (3) described a simplified process of shared decisionmaking about screening by palpation as a reasonable approach for people who come to clinicians with requests for screening and with concerns about their risk of thyroid cancer due to I-131 exposure; (4)
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From page 119... ...
Detection of thyroid nodules I: community practice pattern variation . clinical sk~ll,testaccuracy, rateof false .
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From page 120... ...
. Measures of sensitivity, specificity, and positive predictive value are used to assess the accuracy and efficiency of screening tests in identifying people with and without disease (Table 4.3~.
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From page 121... ...
Condition Condition present absent a+c b+d TABLE 4.4 Importance of Disease Prevalence a+b c+d Legend: a = true positive b = false positive c = false negative d = true negative Testing Conditions: Size of Population = 100,000 Sensitivity of test = 90% Specificity of test = 90% If disease prevalence = 1% Positive Test Negative Test Disease Present Disease Absent 900 (a)
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From page 122... ...
1% Disease 0. 1% 90% 0.009 0.9% No Disease 99.9% 10% 0.999 99.1% Hi= 1.008 ability of disease given a positive test and is the same as in the first part of Table 4.4.
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From page 123... ...
Similarly, after a negative FNA result: Negative Diagnosis Prior ConditionalProduct Revised Cancer 3% 7%21 0.3% No cancer 97% 65%6,305 99.7% ~ = 6,326 The probability of cancer given a negative test decreases from 3 percent to 0.3 percent. Now consider the information provided by an indeterminate or an unsatisfactory FNA result.
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From page 124... ...
. Negative (including indeterminate results)
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