Complexities in the estimation of overdiagnosis in breast cancer screening

Abstract

There is interest in estimating and attributing temporal changes in incidence of breast cancer in relation to the initiation of screening programmes, in particular to estimation of overdiagnosis of breast cancer as a result of screening. In this paper, we show how screening introduces complexities of analysis and interpretation of incidence data. For example, lead time brings forward time-and age-related increases in incidence. In addition, risk factors such as hormone replacement therapy use have been changing contemporaneously with the introduction of screening. Although we do not indicate exactly how such complexities should be corrected for, we use some simple informal adjustments to show how they may account for a substantial proportion of increased incidence, which might otherwise erroneously have been attributed to overdiagnosis. We illustrate this using an example of analysis of breast cancer incidence data from Sweden.

Cancer Screening in the United States, 2010: A Review of Current American Cancer Society Guidelines and Issues in Cancer Screening

“…Although overdiagnosis is likely to be a significant problem in prostate cancer screening, 101 it is most likely a small problem in breast cancer screening, and mostly limited to ductal carcinoma in situ. 57,102 Short-term evaluations of population surveillance data are not a sound basis for judging the effectiveness of screening. 103 As described earlier, both the USPSTF and ACOG recommended beginning screening later, and screening less often, citing less harm from screening when it is done less frequently.…”

Impact of assumptions – the example of the Welch-analysis of mammography screening effectiveness

“…However, screening changes the age-specific incidence in cohorts of women offered screening. This includes a prevalence peak at first screen; an artificial aging at subsequent screens; and a compensatory dip after end of screening [5,6]. Therefore, studies of overdiagnosis require also that women can be followed for a sufficiently long period after end of screening for the compensatory dip to materialize.…”

“…At the start of screening, a prevalence peak is observed, during screening an artificial aging, and when the women have exited screening a compensatory dip will be seen in the incidence [5]. If it takes 2 years to carry out the prevalence screen, around a 100% increase in incidence will be observed during the period [6]. Screening started gradually in the USA, with 17% (aged 50þ) in 1978 having had a mammogram to 74% in 1992 (aged 40þ) [7].…”

Modelling and Inference in Screening: Exemplification with the Faecal Occult Blood Test

“…Some research has been done in the area of over diagnosis. However, the majority of research in this area has been based on observational studies, and mainly in breast cancer (Day, 2005, Duffy et al, 2008, Welch & Black, 2010, Zackrisson et al, 2006, there is little reference to this problem in colorectal cancer. The flaws of using observational studies are obvious: (a) the result based on one study cannot be extended to other scenarios.…”