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Effectiveness of population-based service screening with mammography for women ages 40 to 49 years with high and low risk of breast cancer: socioeconomic status, parity and age at birth of first child
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet.
Umeå University, Faculty of Social Sciences, Centre for Population Studies (CPS). Umeå University, Faculty of Social Sciences, Department of Geography and Economic History, Economic and social geography.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Epidemiology and Global Health.ORCID iD: 0000-0002-5095-3454
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background Whether women in age 40-49 years should be invited to mammography screening or not is debated in many countries and a cost-effective alternative in countries with no screening in age 40-49 years could be selective screening i.e. inviting women at higher risk. In the current study relative effectiveness of mammography screening was estimated for subgroups based on the breast cancer risk factors parity, age at birth of first child and socioeconomic status (SES).

Methods The SCReening of Young women (SCRY) database consist of all women in age 40-49 years in Sweden in 1986-2005 and is split into a study and control group. The study group consists of women in areas where women age 40-49 years were invited to screening and the control group of women in areas where women 40-49 years were not. Rate ratio (RR) estimates were calculated for risk groups. Two exposures were considered; invitation to mammography screening and attendance.

Results There were striking similarities in the RR pattern for women invited to and attending in screening for all three risk factors and there was no statistically significant difference or trend in the RR by risk group. The RR estimates increased by increasing parity for parity 0 to 2 and ranged from 0.55 (95% CI 0.38-0.79) to 0.79 (95% CI 0.65-0.95) for women attending screening. The RR for white collar workers (low SES) was lower than for blue collar workers (high SES), 0.72 (95% CI 0.60-0.86) and 0.79 (95% CI 0.63-0.99) respectively for attending. For women 20-24 years at birth of first child RR was estimated at 0.73 (95% CI 0.58-0.91) for attending and estimates for other ages were similar.

Conclusion There was no statistically significant difference in relative effectiveness of mammography screening by parity, age at birth of first child or socio-economic status.

Keyword [en]
mammography, cancer screening, breast cancer, mortality, risk factors, socioeconomic status, parity
National Category
Cancer and Oncology
Research subject
Oncology
Identifiers
URN: urn:nbn:se:umu:diva-86206OAI: oai:DiVA.org:umu-86206DiVA: diva2:698141
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2015-04-29Bibliographically approved
In thesis
1. Breast cancer screening with mammography of women 40-49 years in Sweden
Open this publication in new window or tab >>Breast cancer screening with mammography of women 40-49 years in Sweden
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Mammografiscreening i ålder 40-49 år i Sverige
Abstract [en]

Background The debate regarding the lower age limit for mammography service screening is old and lively; a product in part of the lower breast cancer risk in younger ages as well as the limited data available for studies of the younger age group. Recently the idea of inviting only high risk groups has gained momentum, however high risk might not be equivalent to greater benefit from screening. Therefore, there is a need for information on effectiveness of screening as it relates to young women and to specific risk groups. To this end, this thesis evaluates mammography screening for the age group – 40 to 49 year old women – in terms of breast cancer mortality reduction in total and in subgroups based on breast cancer risk factors. Overdiagnosis of mammography screening is also evaluated for women 40 to 49 years old. In addition, this thesis presents a statistical method to estimate this effectiveness and to test for differences in effectiveness between subgroups adjusted for non-compliance and contamination.

Methods The studies of this thesis are based on data from the Screening of Young Women (SCRY) database. The SCRY database consists of detailed information on diagnosis, death, screening exposure and risk factors for breast cancer cases and population size by year (between 1986 and 2005) and municipality for women in Sweden between 40 and 49 years old. The material was divided into a study group consisting of the counties that invited women in the age group 40-49 years to mammography screening, and a contemporaneous control group consisting of the counties that did not. Effectiveness was estimated in terms of rate ratios for two different exposures (invitation to and participation in screening), and overdiagnosis for subsequent screening was estimated adjusting for lead time bias. Defining a reference period enabled adjustment for possible underlying differences in breast cancer mortality and incidence. A statistical model for adjusting for non-compliance and contamination in randomised controlled trials was further developed to allow for adjustment in cohort studies using a Poisson model with log-linear structure for exposure and background risk.

Results During the study period (1986-2005), there were 619 and 1205 breast cancer deaths and 6047 and 7790 breast cancer cases in the study group and the control groups, respectively. For women between 40 and 49 years old, the breast cancer mortality reduction was estimated at 26% [95% CI, 17 to 34%] for invited to screening and 29% [95% CI, 20 to 38%] for attending screening. The RR estimates for the high-risk groups based on the risk factors parity, age at birth of first child, and socio-economic status were equal to or higher than that of the low risk groups. The new statistical method showed that the decrease in effectiveness with parity was not a statistically significant trend. The overdiagnosis from subsequent screening for 40 to 49 year old women was estimated at 1% [95 % CI, -6 to 8 %] (i.e., not statistically significant).

Conclusion Subgroup specific effectiveness was also estimated. The relative effectiveness of screening for breast cancer with mammography for women age 40 to 49 years appears to be comparable to that for older women. These findings and the fact that there was no statistically significant overdiagnosis from subsequent screening speak for inviting women 40 to 49 years old to screening. High-risk screening for nulliparous women aged 40 to 49 years, for example, might be an alternative in countries where population-based screening for all women between 40 and 49 years old is not possible. However, the matter of risk factors and the effect of their combinations is complex and risk group screening presents ethical and practical difficulties. The new statistical model is a useful tool for analysing cohorts with exposed and non-exposed populations where non-compliance and contamination is a potential source of bias.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2014. 44 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1661
Keyword
Cohort, mortality, breast cancer, mammography screening, risk factors, parity, age at first birth, socio-economic status, overdiagnosis
National Category
Cancer and Oncology
Research subject
Oncology
Identifiers
urn:nbn:se:umu:diva-86215 (URN)978-91-7459-803-2 (ISBN)
Public defence
2014-03-21, Sal E04, byggnad 6E, Norrlands universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2014-02-28 Created: 2014-02-20 Last updated: 2015-04-29Bibliographically approved

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