CPR For Women and Families - Screening for Breast Cancer with Mammography.

January 2002

Screening for Breast Cancer with Mammography. Letter in The Lancet.

The following letter was published in the December 22/29, 2001 issue of the medical journal The Lancet in reply to an article on mammograms by Ole Olsen and Peter Gotzsche (see reference 1).

Ole Olsen and Peter Gøtzsche's review¹ concurs with the findings of their earlier report² that screening mammography programmes do not reduce breast-cancer mortality and lead to more aggressive treatment. In his Oct 20 Commentary, Richard Horton³ agrees with their conclusion that screening mammography programmes are not therefore justified. These conclusions could have a major effect on women's health care and deserve careful scrutiny.

Our primary criticism is the notion that a screening programme can be justified only if it reduces mortality. Mortality is a very important outcome, and easily measured, and choosing an outcome parameter for ease of measurement is a common bias among clinical investigators. However, outcomes such as quality of life are also important to patients and could justify screening programmes. Unfortunately, such outcomes have been understudied in the assessment of breast-cancer screening. Rather than making assumptions about whether false-positive tests and earlier detection of breast cancer improves or harms quality of life, objective measurement is needed of how mammography screening programmes affect quality of life, and whether certain types of patients will benefit more than others.

Olsen and Gøtzsche conclude that screening mammography leads to overly aggressive treatment. If that is true, it is a condemnation of treatment practices, not of screening. Our organisation is one of many encouraging better education of patients and physicians to lower the prevalence of unnecessarily aggressive treatment. The best solution to improving treatment is better technology, education, and training, along with improved communication between physicians and patients. These strategies deserve more attention from the medical community before a decision is made to eliminate screening programmes that lead to earlier diagnoses. There is no need to throw out the baby with the bath water.

We are also concerned with the meta-analysis itself. In six of seven randomised trials (including the extended Malmö trial⁴) analysed by Olsen and Gøtzsche, a reduction in breast-cancer mortality was associated with the use of screening mammography. We recommend caution before rejecting these findings, which incorporated data from hundreds of thousands of patients, on the basis of one meta-analysis.

Meta-analysis requires many subjective decisions on the selection and weighting of variables. Each decision can introduce bias, no matter how systematic the decision-making process. A second set of investigators carefully analysing the same data might reach very different conclusions. For example, many investigators did not agree with Olsen and Gøtzsche's decision to deem certain clinical trials unreliable on the basis of small baseline differences in mean age between screening and control groups.⁵

Meta-analyses are an evolutionary improvement over the traditional review article, but their limitations must be acknowledged before they are used to formulate major health-policy decisions. The attention garnered by Olsen and Gøtzsche illustrates the need to assess each meta-analysis thoroughly, as well as to reassess the proper role of meta-analyses.
*Jae Hong Lee, MD, MPH
Diana Zuckerman, Ph.D.

National Center for Policy Research for Women and Families, 1901 Pennsylvania Avenue, Suite 901, Washington, DC 20006, USA (e-mail:jl@center4policy.org)

1 Olsen O, Gøtzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001; 358: 1340-42.

2 Gøtzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet 2000; 355: 129-34.

3 Horton R. Screening mammography--an overview revisited. Lancet 2001; 358: 1284-85.

4 Andersson I, Janzon L. Reduced breast cancer mortality in women under age 50: updated results from the Malmo Mammographic Screening Program. J Natl Cancer Inst Monogr 1997; 22: 63-67.

5 Hayes C, Fitzpatrick P, Daly L, Buttimer J. Screening mammography re-evaluated. Lancet 2000; 355: 749.

Reprinted with permission from Elsevier Science (The Lancet 2001, 358:2164-2165).

Single copies of this article can be downloaded and printed for the reader's personal research and study by clicking here and selecting the article titled, "Screening for breast cancer with mammography," in the Correspondence section.

For more information, visit the home pages of The Lancet and ScienceDirect.

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