Affiliations of authors: Applied Research Program, National Cancer Institute, Rockville, MD (SHT); Cancer Research and Biostatistics, University of Washington, Seattle (WEB); Group Health Cooperative, Seattle, WA (WEB, EW, LI); Henry Ford Health System, Detroit, MI (MU-Y); Kaiser Permanente Southern California, Pasadena, CA (AMG); Kaiser Permanente Colorado, Denver, CO (KB)
Correspondence to: Stephen H. Taplin, MD, MPH, Applied Research Program, National Cancer Institute, 6310 Executive Blvd., Rockville, MD 208527344 (e-mail: Taplins{at}mail.nih.gov).
Our recent study (1) of the implementation of mammography in integrated health systems stimulated criticism by Dr. Baum (2) for failing to recognize the tautology that screen-detected cancers are good, interval cancers are bad, and "noncompliant" women tend to have bad disease. Regarding his interpretation of our study, Baum concluded that "I could be wrong."
We agree with his final conclusion. Our paper evaluated the implementation of mammography and not the technology itself, so his tautology and preamble about biases are tangential to our work. Lead time is necessary for screening to be efficacious, but lead time bias is a concern when evaluating survival, which we did not do (3). Length bias occurs when conclusions are drawn about all cancers from those found at screening (3), but our study included late-stage cancers found by any means, and our purpose was to examine priorities for improving implementation. Dr. Baum suggests that encouraging women of low income to be screened will dilute screening's effect, because social class reduces survival (5). The evidence he provides for this poor prognosis is the hazard ratio (HR) for death associated with lowsocial class postal codes in a survival analysis confounded by lead time bias (HR = 1.23, 95% confidence interval = 0.96 to 1.56). That hazard ratio is consistent with no effect and is not elevated for the other social strata (4). We agree that low income does reduce the likelihood of obtaining screening in the United States, primarily because of lack of health insurance (5). However, the low-income women in this study had health insurance through plans that will continue to offer screening mammography to all women. Those plans could begin to evaluate why low-income women are less likely to take advantage of the offer to be screened.
We concluded that late-stage disease might be further reduced by improvements in screening implementation, but we did not estimate its effect on mortality and pointed out that the mortality reduction is unlikely to be the same as results in trials. We assumed a benefit for mammography among women aged 5074 years but also assumed that the benefit is small enough that it is important to do screening correctly. We therefore evaluated where the screening process broke down using a widely recognized methodology and the knowledge that observational designs provide valid results in many cases (6).
Given high screening rates, and the evidence for breakdowns in follow-up after screening, we hypothesized that we might find high proportions of women with delayed diagnoses after positive screens. However, we found high proportions of late-stage cancers associated with an absence of screening and with negative screens between 1 and 3 years before diagnosis. Dr. Baum suggests that these are all interval cancers, but 17% were found by screening, and other work has shown that 31% of cancers occurring within 2 years of a negative screen were visible at screening (7). Shortening the screening interval and improving detection might change the prognosis for these women, although we agree that we do not know the magnitude of that change.
As noted in our Methods section, we chose large tumors because they would help identify screening implementation failures in a way that would help set priorities for improvement. Both large tumors and metastatic tumors decrease in incidence with screening implementation, so their occurrence can serve as an indication of failures in the screening process (1). Now we know where there is the greatest opportunity for improvement and where more research is needed.
NOTES
Editor's note: Dr. Baum declined to respond.
REFERENCES
(1) Taplin SH, Ichikawa L, Ulcickas-Yood M, Manos MM, Geiger AM, Weinmann S, et al. Reason for late-stage breast cancer: absence of screening or detection, or breakdown in follow-up? J Natl Cancer Inst 2004;96:151827.
(2) Baum M. Breast cancer screening comes full circle. J Natl Cancer Inst 2004;96:14901.
(3) Taplin SH, Mandelson MT. Principles of cancer screening for clinicians. Prim Care 1992;19:51333.[ISI][Medline]
(4) Kaffashian F, Godward S, Davies T, Solomon L, McCann J, Duffy S. Socioeconomic effects on breast cancer survival: proportion attributable to stage and morphology. Br J Cancer 2003;89:16936.[CrossRef][ISI][Medline]
(5) Lawson HW, Henson R, Bobo JK, Kaeser MK. Implementing recommendations for the early detection of breast and cervical cancer among low-income women. MMWR Recomm Rep 2000;49(RR02):3755.[Medline]
(6) Concato J, Shah N, Horwitz RI. Randomized, controlled trials, observational studies, and the hierarchy of research designs. N Engl J Med 2000;342:188792.
(7) Porter PL, El-Bastawissi AY, Mandelson MT, Lin MG, Khalid N, Watney EA, et al. Breast tumor characteristics as predictors of mammographic detection: comparison of interval and screen-detected cancers. J Natl Cancer Inst 1999;91:20208.
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