DÄ internationalArchive23/2008Benefit and Risk of Mammography Screening – Considerations from an Epidemiological Viewpoint: Randomized Controlled Trials Are Needed

Correspondence

Benefit and Risk of Mammography Screening – Considerations from an Epidemiological Viewpoint: Randomized Controlled Trials Are Needed

Dtsch Arztebl Int 2008; 105(23): 421. DOI: 10.3238/arztebl.2008.0421c

Mühlhauser, I

LNSLNS The authors' attempt to show why mammography screening should be evaluated on the basis of epidemiological studies rather than randomized controlled clinical trials (RCTs). Yet it is precisely because an epidemiological assessment is not possible that RCTs are needed according to internationally accepted standards. Furthermore, RCTs do indeed exist for mammography screening, as does a high-quality Cochrane Review by an independent group of authors (1).

Epidemiological analyses tend to overstate the benefit of screening for the following reasons (2):

(1) Screened women differ from unscreened women. They are a priori healthier and better educated and therefore have a better chance of survival, both in general and for the particular disease for which they are being screened.

(2) Screening tends to detect relatively benign and slowly growing tumors.

(3) Early diagnosis often merely means prolonging the time that the patient lives with breast cancer, rather than improving the prognosis.

(4) Screening detects cases of breast cancer that would never have come to attention without it (overdiagnosis). It is thus inappropriate to compare a group of women whose cancers were diagnosed by screening to a group of unscreened women whose cancers came to medical attention in other ways. It should come as no surprise, therefore, that the Cochrane Review estimates the benefit of mammography screening to be much less, and the resulting harm to be much greater, than stated by Becker and Junkermann (1, 3).

The authors argue that the harm due to breast cancer itself ought to be taken into consideration. When such calculations are made, however, overdiagnoses must be considered also, as well as the overall death rate due to cancer and the overall mortality. These are not improved by screening (1, 3). The low sensitivity of mammography screening in the German pilot projects is not mentioned either (3); this reduces the benefit of screening. DOI: 10.3238/arztebl.2008.0421c


Prof. Dr. med. Ingrid Mühlhauser
Universität Hamburg
MIN Fakultät, Fachwissenschaft Gesundheit
Marthin-Luther-King Platz 6, 20146 Hamburg, Germany
ingrid_muehlhauser@uni-hamburg.de
1.
Gotzsche P, Nielsen M: Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006, Issue 4. MEDLINE
2.
Sackett DL, Haynes RB, Guyett GH, Tugwell P: Clinical epidemiology. A basic science for clinical medicine. 2nd edition. Little, Brown and Company. Boston, Toronto, London 1991.
3.
Mühlhauser I: Ist Vorbeugen besser als Heilen? Dtsch Arztebl 2007; 104: A 1805–7. VOLLTEXT
1. Gotzsche P, Nielsen M: Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006, Issue 4. MEDLINE
2. Sackett DL, Haynes RB, Guyett GH, Tugwell P: Clinical epidemiology. A basic science for clinical medicine. 2nd edition. Little, Brown and Company. Boston, Toronto, London 1991.
3. Mühlhauser I: Ist Vorbeugen besser als Heilen? Dtsch Arztebl 2007; 104: A 1805–7. VOLLTEXT