Advanced breast cancer incidence following population-based mammographic screening

January 28, 2011

Study Design:  Systematic review of published data from January 1990 to June 2009 on incidence trends of advanced breast cancer in areas with mammography screening for at least 7 years and high rates of screening participation.   Data from the literature was supplemented with data from several population-based cancer registries.

Study Eligibility:  Data or studies that reported a time trend of advanced invasive breast cancer incidence in the general population, with information on cancer size or stage.  Other inclusion criteria were incidence reported for at least 7 years after screening began, and screening attendance in the target group of ≥60% during at least the last 3-4 years of observation.  Exclusion criteria was reporting of size or stage as a percentage of total number of cases, and obtaining results by application of models to cancer registry data. 

Enrollment:  Data from eight published studies, a report issued by the Dutch National Evaluation Team for Breast Cancer Screening, as well as data collected by the following cancer registries:  Tasmania, Northern Ireland, Scottish, the nine oldest SEER areas, and the NCI’s Historical Connecticut Tumor Registry.

Research Question:  Does mammography screening reduce the incidence of advanced breast cancer?

Many studies have investigated the impact of mammography screening on the observed reduction in breast cancer mortality; however the challenge of separating the impact of screening and newer, more efficacious treatments on mortality remains.  Mammography screening alone would impact breast cancer mortality through earlier diagnosis, thus decreasing the number of more advanced cancers found in years after screening began.  In this systematic review of published data, Autier et al. explored the impact of screening on the incidence of advanced breast cancer.

The researchers conducted a systematic review of data published from January 1990 to June 2009 on incidence trends of advanced breast cancer in areas with mammography screening for at least 7 years and high rates of screening participation.   Data from eight studies was supplemented with data from several population-based cancer registries (Tasmania, Northern Ireland, Scotland, the nine oldest SEER registries– Connecticut, Hawaii, Iowa, New Mexico, Utah, Atlanta, Detroit, San Francisco-Oakland, and Seattle-Puget Sound, and NCI’s Historical Connecticut Tumor Registry).  A report issued by the Dutch National Evaluation Team for Breast Cancer Screening was also included in this analysis.  Advanced cancers were considered tumors ≥ 20mm in size (T2 or above in the TNM staging schema), or stage II-IV.  Annual percent changes (APC) and 95% confidence intervals depicted the age-adjusted incidence rates of advanced breast cancer over time.    

The percentage of eligible women participating in mammography screening was high in all areas, ranging from 60% to 88%.  Age-adjusted APCs were stable or increasing (APCs of -0.5% to 1.7%) after implementation of mammography screening in the following areas: Northern Ireland, Scotland, Norway and Geneva (Switzerland), New Mexico, Rhode Island, and Australia.  However, in Firenze (Italy), the Netherlands, SEER and Connecticut, there were downward trends in the APCs followed by increases back to pre-screening rates.  In many of these areas, the downward trend was observed in years preceding screening and before participation to screening was substantial. 

Limitations of this study include lack of published data on breast cancer incidence by size or stage, which the authors have identified as an area of improvement for cancer registries.  Also, in some areas, incidence rates were reported for a wider age group than the target group for screening. 

Screening is often praised for its ability to reduce breast cancer mortality without evidence that this is actually true.  These results do not support a role of mammography screening in reducing breast cancer mortality.  Early detection through colorectal and cervical cancer screening has resulted in substantially fewer advanced cancers for these diseases, contributing to the cancer-specific mortality reductions.  Further research is needed to determine what factors have contributed to the decline in breast cancer mortality since 1990. 

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