Overdiagnosis in organised mammography screening in Denmark. A comparative study

Karsten J Jørgensen,Per-Henrik Zahl,Peter C Gøtzsche

doi:10.1186/1472-6874-9-36

Karsten J Jørgensen, Per-Henrik Zahl + Show 1 more

Open Access

https://doi.org/10.1186/1472-6874-9-36

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Abstract

BackgroundOverdiagnosis in cancer screening is the detection of cancer lesions that would otherwise not have been detected. It is arguably the most important harm. We quantified overdiagnosis in the Danish mammography screening programme, which is uniquely suited for this purpose, as only 20% of the Danish population has been offered organised mammography screening over a long time-period.MethodsWe collected incidence rates of carcinoma in situ and invasive breast cancer in areas with and without screening over 13 years with screening (1991-2003), and 20 years before its introduction (1971-1990). We explored the incidence increase comparing unadjusted incidence rates and used Poisson regression analysis to compensate for the background incidence trend, variation in age distribution and geographical variation in incidence.ResultsFor the screened age group, 50 to 69 years, we found an overdiagnosis of 35% when we compared unadjusted incidence rates for the screened and non-screened areas, but after compensating for a small decline in incidence in older, previously screened women. Our adjusted Poisson regression analysis indicated a relative risk of 1.40 (95% CI: 1.35-1.45) for the whole screening period, and a potential compensatory drop in older women of 0.90 (95% CI: 0.88-0.96), yielding an overdiagnosis of 33%, which we consider the most reliable estimate. The drop in previously screened women was only present in one of the two screened regions and was small in absolute numbers.DiscussionOne in four breast cancers diagnosed in the screened age group in the Danish screening programme is overdiagnosed. Our estimate for Denmark is lower than that for comparable countries, likely because of lower uptake, lower recall rates and lower detection rates of carcinoma in situ.

Highlights

Overdiagnosis in cancer screening is the detection of cancer lesions that would otherwise not have been detected
We studied whether the increase in incidence in women who were offered screening was compensated by a drop in breast cancer incidence when the women passed the age limit for screening, and compared with the development in women in the same age group in areas without screening, and with that in younger women
Among women in the screened age group, pre-screening breast cancer incidence increased at a stable rate from 1971-1990 (Fig. 1), with slightly higher rates in the screened areas than in the non-screened areas (Table 1)

Summary

Introduction

Overdiagnosis in cancer screening is the detection of cancer lesions that would otherwise not have been detected It is arguably the most important harm. Overdiagnosis in cancer screening is defined as the detection of cancers that would otherwise not have been detected in the remaining life-span of the individuals [1]. It is mainly caused by the detection of slow-growing cancers that do not manifest clinically before people die from (page number not for citation purposes). Overdiagnosis is a problem with mammography screening, but it has been been omitted in most information material intended to help women make informed decisions about participation [6,7,8]

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