Public Health Focus: Mammography

Among U.S. women, breast cancer is the most commonly diagnosed cancer and the second leading cause of death from cancer. From 1980 through 1987, the incidence of breast cancer increased from 94.6 to 124.3 per 100,000 women (age-adjusted to the 1990 U.S. population) (1). In contrast, death rates remained stable; during 1988, 31.1 per 100,000 U.S. women died from the disease (Table 1) (2,3). Although the prognosis for breast cancer is more favorable than for many other types of cancers, breast cancer continues to be an important source of years of potential life lost before age 65 (YPLL) (Table 1). White women account for 82% of all YPLL from breast cancer; however, the estimated rate of YPLL during 1988 was approximately 25% higher for black women than white women. For breast cancer, certain primary risk factors (e.g., family history, age at menarche, and age at menopause) cannot be altered and others (e.g., parity and age at first pregnancy) are not practical targets for intervention. Therefore, as a secondary method for prevention of breast cancer, mammography screening is the most commonly recommended intervention. During 1990, 58% of U.S. women aged greater than or equal to 40 years reported having had a screening mammogram within the preceding 2 years (Figure 1). This report summarizes information regarding the efficacy, effectiveness, and cost-effectiveness of mammography screening. Efficacy

Results from large randomized clinical trials indicate that mammography screening has had favorable effects on breast-cancer mortality (Table 2). In these randomized trials that compared all women invited to screening (regardless of whether they participated) with an uninvited control group, mortality was reduced among women aged 50-69 years who were invited to screening. Among women who complied with the screening recommendations, calculations from the combined published data suggest a reduction in mortality of approximately 39% (4). These findings are consistent with studies with nonrandomized controls, comparisons to national rates, and several case-control studies on mammography screening. Although no studies have shown a statistically significant reduction in the risk for dying from breast cancer among women aged 40-49 years, more studies show a favorable trend for screening than studies showing no trend or harmful effects from screening for this age group (5). Effectiveness

Data from the randomized trials have been used to estimate population mortality reductions that could be achieved through routine mammography programs (6-9). The estimated breast-cancer mortality reduction has ranged from 8% to 40%, reflecting different assumptions among the mathematical models about targeted age groups, screening intervals, sensitivity of the mammography, compliance with regular screening, and natural history of the disease. Among women who receive screening regularly, the mortality reduction should be substantially greater than these population estimates. Cost-effectiveness

Estimates of the cost-effectiveness of mammography vary widely because of differences in methodologies, measures, assumptions, and the programs and policies evaluated. Factors affecting the estimates include the proportion of high-risk women screened, the sensitivity and specificity of the mammography technique, the interval between examinations, and the cost of each mammogram. In the Netherlands -- where invitations were mailed to participants -- the annual screening of women aged 50-69 years was estimated at a cost of $14,800 per life year gained (6). Simulated models based on the United Kingdom experience that assumed relatively low sensitivity and participation rates estimated costs ranging from $4500 to $5500 per life year saved (8). Estimates using data from the U.S. Breast Cancer Detection Demonstration Project (BCDDP) (9) showed that annual screening of women aged 55-65 years with physical examination and mammography yielded a marginal cost of $22,000 per life year saved. Data from a 1960s trial that used less sensitive radiologic technology (the Health Insurance Plan of Greater New York (HIP)) indicated the estimated cost of saving one life year was less than or equal to $84,000. For women aged greater than 65 years, the estimated cost per life year saved ranged from $13,200 to $28,000. Estimates of the cost per life year saved among women aged 40-49 years ranged from $30,000 (BCDDP data) to $135,000 (HIP data) (10). However, screening programs with mortality reduction estimates as low as 8%-12% can be cost-effective (based on assumptions of lower sensitivity than shown in the most successful trials and participation rates of 50%-70%) (6,8).

The estimated annual cost of illness for breast cancer is $3.8 billion, including $1.8 billion for medical-care costs (converted to 1987 dollars) (11). During the 1980s, in place of radical mastectomies, modified radical mastectomy and breast-preservation techniques were increasingly performed and contributed to a reduction in the average number of hospital days associated with the treatment for breast cancer (in 1982, an average of 10.0 days compared with 4.6 days during 1990) (Table 1). Reported by: A Elixhauser, Battelle, Arlington, Virginia. Div of Cancer Prevention and Control, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: Widespread mammography screening may explain, in part, the increasing breast-cancer incidence in the United States; however, this increase also occurred among population groups not covered by screening and among industrialized countries before mammographic screening had been widely implemented. Screening with either mammography alone or in combination with physical breast examination can reduce the disease burden from breast cancer by reducing both morbidity and mortality. Breast-cancer screening studies illustrate that 1) high-quality mammography is needed to ensure breast tumors are diagnosed at a stage early enough to reduce mortality and 2) quantitative measures are available and can be used to evaluate and improve screening programs (12).

Differences in sensitivity of the screening tests might explain some of the differences in mortality reduction in different screening trials. Although data are not available on mortality reductions obtained from routine mammography screening that are not part of research programs, preliminary data from extensive screening programs are available from Australia, the Netherlands, and Scandinavia. Overall results indicate that acceptable levels of sensitivity and specificity of mammography can be achieved and suggest that these programs may result in a future reduction of breast-cancer mortality. However, early results from the carefully monitored national program in Finland (13) indicate that the sensitivity of mammography is 25%-50% lower than that measured in the major screening trials, highlighting the difficulty in maintaining high-quality imaging and interpretation.

Age is considered the only practical criterion on which to base screening guidelines. Targeting screening to only women who have one or more of the established breast-cancer risk factors would allow for 20%-50% of breast cancers to remain undetected by screening and, therefore, would undermine the cost-effectiveness of screening. Because of reduced sensitivity of screening and a lower incidence of breast cancer among younger women, the cost-effectiveness of screening younger women is less favorable than for older women. Mammography screening trials have not convincingly demonstrated mortality reduction among women less than 50 years of age. However, if more sensitive screening methods are developed, the cost-effectiveness of screening younger women might be improved. In addition, the value of screening women aged greater than or equal to 70 years has not been adequately addressed; whether cost-effective programs can be developed and successfully implemented for women aged greater than or equal to 70 years must be determined.

In addition, the optimum interval for mammography screening has not been firmly established; the best estimates are based on indirect calculations (14). However, further data regarding this question of screening interval may be provided through long-term follow-up of the randomized clinical trials and mathematical modeling techniques and from a recently initiated clinical trial in the United Kingdom.

If routine screening programs are to have the favorable impact in reducing breast-cancer mortality as observed in randomized clinical trials, breast-cancer screening programs should have monitoring systems and require strict adherence to quality-assurance guidelines. Effective tracking and reminder systems must be an integral part of breast-cancer screening programs. In addition, if the benefits of early treatment are to be assured for women with a screening-detected cancer, physicians and health-care organizations must ensure timely referrals to diagnose and treat all women with abnormal screening results. Experiences from cervical cancer screening programs indicate that operational constraints on follow-up of abnormal screening exams can jeopardize the entire benefit of the program (15).

Mammography can be highly sensitive and specific, and can be provided at reasonable cost for widespread screening of asymptomatic women. In addition to the implementation of high-quality screening programs, however, evaluations of cost-effectiveness should be incorporated into these programs as well as additional research to better quantify the contribution of mammography screening in reducing mortality and morbidity in varied community settings.

References

1. National Cancer Institute. Cases diagnosed between 1973 and 1987 and intercensal population estimates by race, sex, and age (machine-readable public-use data tapes). Bethesda, Maryland: US Department of Health and Human Services, Public Health Service, National Institutes of Health, 1990.

2. Irwin R. Intercensal estimates of the population by age, sex, and race (machine-readable public-use data tapes). Alexandria, Virginia: Demo-Detail, 1980-1988.

3. NCHS. Vital statistics mortality data, multiple cause-of-death detail (machine-readable public-use data tapes). Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1973-1988.

4. Day NE. Screening for breast cancer. Br Med Bull 1991;47:400-15.

5. Shapiro S. Periodic breast cancer screening in seven foreign countries. Cancer 1992;69(suppl):1919-24.

6. Van der Maas PJ, de Koning HJ, van Ineveld BM, et al. The cost effectiveness of breast cancer screening. Int J Cancer 1989;43:1055-60.

7. Prorok PC. Mathematical models of breast cancer screening. In: Day NE, Miller AB, eds. Screening for breast cancer. Toronto: Hans Huber Publishers, 1988:95-104. (International Union Against Cancer monograph).

8. Knox EG. Evaluation of a proposed breast cancer screening regimen. Br Med J 1988;297:650-4.

9. Eddy DM. Screening for breast cancer. Ann Intern Med 1989;111:389-99.

10. Eddy DM, Hasselblad V, McGivney W, Hendee W. The value of mammography screening in women under age 50 years. JAMA 1988; 259:1512-9.

11. Scitovsky AA, McCall N. Economic impact of breast cancer. Frontiers of Radiation Therapy and Oncology 1976;11:90-101.

12. Day NE, Williams DRR, Khaw KT. Breast cancer screening programmes: the development of a monitoring and evaluation system. Br J Cancer 1989;59:954-8.

13. Hakama M, Elovainio L, Kajantie R, Louhivuori K. Breast cancer screening as public health policy in Finland. Br J Cancer 1991;64:962-4.

14. Tabar L, Fagerberg G, Day NE, Holmberg L. What is the optimum interval between mammographic screening examinations? -- an analysis based on the latest results of the Swedish Two-County Breast Cancer Screening Trial. Br J Cancer 1987;55:547-51.

15. Anonymous. Cancer of the cervix: death by incompetence (Editorial). Lancet 1985;2:363-4.

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