CORRESPONDENCE

RESPONSE: Re: Detection of Ductal Carcinoma In Situ in Women Undergoing Screening Mammography

Rachel Ballard-Barbash, William E. Barlow, Virginia L. Ernster
for the Breast Cancer Surveillance Consortium

Affiliations of authors: R. Ballard-Barbash, Applied Research Program, Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD; W. E. Barlow, Center for Health Studies, Group Health Cooperative, Seattle, WA; V. L. Ernster, Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco.

Correspondence to: Rachel Ballard-Barbash, M.D., M.P.H., Applied Research Program, Division of Cancer Control and Population Sciences, National Cancer Institute, EPN 4005, 6130 Executive Blvd., Bethesda, MD 20892–7344 (e-mail: barbashr{at}mail.nih.gov).

Contrary to the suggestion by Dr. Kopans, we did not indicate that we were the first to observe that ductal carcinoma in situ (DCIS) rates increase with age while the proportion of all breast cancers that are DCIS declines with age. Although we cited a number of previous reports that provided DCIS rates in screened populations and the percentage of DCIS cases among all breast cancers, prior reports (16) have not stressed the difference in the direction of DCIS rates and percentages with age. The cited article by Kopans et al. (7) did not address the same issues that we did. Percentages of DCIS in their article were based on 4778 biopsies performed among women undergoing mammography. In contrast, our data were based on all women undergoing screening mammography, not just women having biopsies, which enabled us to produce population-based measures. Analyzing data from 653 833 screening mammograms for positive and negative mammograms separately, we reported data on DCIS detection rates by age and the percentage of all breast cancers that were DCIS. Thus, the finding of Kopans et al. (7) that the percentage of biopsies that proved to be DCIS increased with age is not the same as our finding that the rate of DCIS per 1000 mammograms increased with age.

The decreasing proportion of DCIS cases among all breast cancers with age in both of our studies may represent progression to invasive disease with age; however, neither their data nor ours can address that hypothesis directly. Were the progression hypothesis correct, one might have expected declines (over time) in invasive breast cancer incidence following the observed increases in DCIS incidence, similar to the declines in invasive cervical cancer that followed widespread use of the Pap test. However, such declines in invasive breast cancer incidence have not occurred; thus, a more direct test of the progression hypothesis is needed. Our point in contrasting the different age trends for proportions and rates of screen-detected DCIS was to illustrate the inappropriateness of concluding that risk of DCIS is greater in younger women simply because the proportion of all breast cancers that is DCIS decreases with age.

Dr. Kopans is correct in commenting that there is no discontinuity in the incidence of cancer at age 50 years, just as there is no discontinuity at any other age where one may contemplate starting screening (e.g., age 40 years). However, Dr. Kopans is incorrect in assuming that there is no scientific rationale underlying decisions about the optimal age to begin screening. The overall breast cancer rate (i.e., DCIS and invasive) per 1000 screens and the cancer detection rate (i.e., positive screen) per 1000 screens by age, which are based on data from the population-based Breast Cancer Surveillance Consortium, are shown in Fig. 1Go, A. The discrepancy between the two graphs reflects the interval or missed cancer rate. Fig. 1Go, B, shows the ratio of the two rates or sensitivity of screening mammography, which is somewhat lower in the younger age groups. Thus, the benefit of screening increases with age due to both higher incidence and better sensitivity of mammography. Therefore, there exist tradeoffs for risk and benefit by age. Choosing benchmark ages, such as 40 or 50 years, is convenient for public health messages because the actual optimal year of age for screening may not be a memorable value. However, a complex determination of risks and benefits underlies this choice, as does an expectation for judicious use of health care resources and a need to maintain the public’s trust in recommendations from medical professionals.



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Fig. 1. A ) Breast cancer incidence rate and screen-detected cancer rate by age per 1000 screening mammograms. Filled triangles = overall cancer rate per 1000 screening mammograms. Open circles = screen-detected cancer rate per 1000 screening mammograms. B) Sensitivity of screening mammography by age. Smoothed lowess curves are fit to the points to show the trends.

 

NOTES

Editor’s note: The incidence and mortality rates used in the Stat Bite (1) are taken directly from Table IV-4 of The National Cancer Institute’s Cancer Statistics Review: 1973–1999 (2). That table reports Surveillance, Epidemiology, and End Results (SEER)1 Program incidence and U.S. death rates for breast cancer for all women, women younger than 50 years, and women aged 50 years and older. The Stat Bite based on this data shows trends in incidence and mortality over time as reported by SEER. Age-specific rates, which were not the subject of this Stat Bite, are available in Tables IV-2 and IV-3 of the Cancer Statistics Review (2).

  1. Stat Bite: incidence of and mortality from breast cancer, 1973–1999. J Natl Cancer Inst 2002;94:1524.[Free Full Text]

  2. Ries LA, Eisner MP, Kosary CL, Hankey BF, Miller BA, Clegg L, et al., editors. SEER cancer statistics review, 1973–1999. National Cancer Institute. Bethesda (MD): 2002. Available at: www.http://seer.cancer.gov.csr/1973_1999/.

1 SEER is a set of geographically defined, population-based, central cancer registries in the United States, operated by local nonprofit organizations under contract to the National Cancer Institute (NCI). Registry data are submitted electronically without personal identifiers to the NCI on a biannual basis, and the NCI makes the data available to the public for scientific research. Back

REFERENCES

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2 Organized Breast Cancer Screening Programs in Canada: 1996 report. Laboratory Centre for Disease Control, Health Canada. Minister of Public Works and Government Services Canada; 1999.

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