Effect of mammographic service screening on stage at presentation of breast cancers in Sweden

Abstract

BACKGROUND.Previous results have shown a reduction in mortality with service screening in Sweden on the order of 40%. If the rate of tumors at a later stage were similarly reduced, this would give further support to the mortality findings.METHODS. The rates of lymph node-positive cancers, of tumors >2 cm in pathological size, and of tumors of TNM stage II or worse before and after the introduction of screening were compared in 13 areas in Sweden, adjusted for changes in overall incidence during the period of study and stratified by age (40-49 and 50-69 years). CONCLUSIONS. Screening has significantly and substantially reduced the rates of larger tumors and lymph node-positive breast cancer in Sweden, and the magnitude of the reduction is consistent with the reduction in breast cancer mortality. RESULTS.

The impact of mammography screening programmes on incidence of advanced breast cancer in Europe: a literature review

“…The papers from Finland, the West Midlands region of the UK, and Ireland reported programmes aimed at women aged 50–59 years [34] and 50–64 years [13, 42]. The target age of the Swedish programme varied locally between 40 and 74 years [33]. The size of the target population, often not reported, was between 500,000 and 1,000,000 in the national Dutch study [14], in the Danish studies [8, 37] and in one Italian study [15], and exceeded 1,000,000 in the study from Sweden [33] and in a second study from Italy [32].…”

“…The target age of the Swedish programme varied locally between 40 and 74 years [33]. The size of the target population, often not reported, was between 500,000 and 1,000,000 in the national Dutch study [14], in the Danish studies [8, 37] and in one Italian study [15], and exceeded 1,000,000 in the study from Sweden [33] and in a second study from Italy [32]. The screening interval was 24 months except in the West Midlands (36 months) [13].…”

“…Because there is a latency for the effect of screening on ABCR to take place, at any point in time there are women (i.e., new quinquagenarians, new immigrants, and late attendees) with insufficient exposure time.The effect of screening on ABCR is underestimated, due to a disproportionate influence of prevalence screens.All studies3Pace of implementationPublic health screening programmes are implemented gradually, in a markedly stepwise fashion, since large populations are divided in distinct administrative units each targeted by an independent local plan of action.The effect of screening on ABCR is diluted. Until implementation is completed, there are women who are diagnosed with breast cancer before being invited, and who greatly contribute to ABCR.[8, 14, 15, 19, 29, 30, 32, 33, 36–39, 44]4Prevalence effectThe prevalence screen may be associated with a transient increase in ABCR [13]. During a stepwise implementation of the programme, when the time elapsed from the start is theoretically sufficient to see a decrease in ABCR, this is counteracted by an opposite effect due to newly enrolled women – especially if invitations increase over time.[8, 14, 15, 19, 29, 30, 32, 33, 36–39, 44]5Reference incidence (i)The reference (or underlying) incidence rate, with which to compare the rate observed after the introduction of screening, is not known with precision [49].…”

“…The increase in node-positive disease is likely to be population-specific and will depend on the rate of change of local surgical policy. However, reductions in node-positive disease as a results of screening are likely to be underestimated rather than overestimated due to the stage migration.[12–14, 19, 29–43]9Missing data on tumour stageWhatever staging system is being used, the introduction of a screening programme tends to bring an improved quality of breast cancer registration, with a sharp decrease in the proportion of unknown-stage cancers.Because more cases are increasingly placed in all known-stage categories, an apparent increase in all stage-specific rates occurs – including ABCR.[8, 15, 30, 32, 33, 38, 39]10Statistical approachThe statistical approach is not standardised, and includes the provision of purely descriptive information and the use of methods which are difficult to interpret, such as joinpoint analysis.Descriptive information does not allow evaluation of the magnitude and significance of observed changes in ABCR. Methods like the joinpoint analysis are useful for assessing the points in time when ABCR begins to decrease and when it stabilizes, but may be misleading when used to assess the significance of the trend.…”

Increased breast cancer screening and downstaging in Colombian women: A randomized trial of opportunistic breast‐screening

“…While mortality is the end‐point by which screening programs should ultimately be judged, the rate of later‐stage tumors can be used as a reliable surrogate indicator of the effect of a screening program before mortality results are available 24, 25. The lack of long‐term follow‐up in our study meant we were unable to ascertain whether this will translate to reductions in mortality; we also are not able to address the frequency of interval cancers (cancers diagnosed during the interval between screening episodes) using this opportunistic approach.…”