Benefits and harms of breast cancer screening: Cohort study of breast cancer mortality and overdiagnosis

BACKGROUND

Quantifying the benefits and harms of breast cancer screening accurately is important for planning and evaluating screening programs and for enabling women to make informed decisions about participation. However, few cohort studies have attempted to estimate benefit and harm simultaneously.

AIMS

We aimed to quantify the impact of mammographic screening on breast cancer mortality and overdiagnosis using a cohort of women invited to attend Australia's national screening program, BreastScreen.

METHODS

In a cohort of 41,330 women without prior breast cancer diagnosis, screening, or diagnostic procedures invited to attend BreastScreen Western Australia in 1994-1995, we estimated the cumulative risk of breast cancer mortality and breast cancer incidence (invasive and ductal carcinoma in situ) from age 50 to 85 years for attenders and non-attenders. Data were obtained by linking population-based state and national health registries. Breast cancer mortality risks were estimated from a survival analysis that accounted for competing risk of death from other causes. Breast cancer risk for unscreened women was estimated by survival analysis, while accounting for competing causes of death. For screened women, breast cancer risk was the sum of risk of being diagnosed at first screen, estimated using logistic regression, and risk of diagnosis following a negative first screen estimated from a survival analysis.

RESULTS

For every 1,000 women 50 years old at first invitation to attend BreastScreen, there were 20 (95% CI 12-30) fewer breast cancer deaths and 25 (95% CI 15-35) more breast cancers diagnosed for women who attended than for non-attendees by age 85. Of the breast cancers diagnosed in screened women, 21% (95% CI 13%-27%) could be attributed to screening.

DISCUSSION

The estimated ratio of benefit to harm was consistent with, but slightly less favourable to screening than most other estimates from cohort studies.

CONCLUSION

Women who participate in organised screening for breast cancer in Australia have substantially lower breast cancer mortality, while some screen-detected cancers may be overdiagnosed.

Extending Age Ranges in Breast Cancer Screening in Four European Countries: Model Estimations of Harm-to-Benefit Ratios

Simple Summary

Breast cancer screening causes harms and benefits. The balance between the two varies by age. By applying microsimulation modelling, we compared several age ranges of screening in four European countries (the Netherlands, Finland, Italy and Slovenia) and evaluated the respective harm-to-benefit ratios. In all countries, adding screening between the ages 45 and 49 or 70 and 74 resulted in more life-years gained and more breast cancer deaths averted, but at the expense of increases in harms. Adapting the age range of breast cancer screening is an option to improve harm-to-benefit ratios in all four countries. The prioritization of considered harms and benefits affects the interpretation of results.

Abstract

The main benefit of breast cancer (BC) screening is a reduction in mortality from BC. However, screening also causes harms such as overdiagnosis and false-positive results. The balance between benefits and harms varies by age. This study aims to assess how harm-to-benefit ratios of BC screening vary by age in the Netherlands, Finland, Italy and Slovenia. Using microsimulation models, we simulated biennial screening with 100% attendance at varying ages for cohorts of women followed over a lifetime. The number of overdiagnoses, false-positive diagnoses, BC deaths averted and life-years gained (LYG) were calculated per 1000 women. We compared four strategies (50–69, 45–69, 45–74 and 50–74) by calculating four harm-to-benefit ratios, respectively. Compared to the reference strategy 50–69, screening women at 45–74 or 50–74 years would be less beneficial in any of the four countries than screening women at 45–69, which would result in relatively fewer overdiagnoses per death averted or LYG. At the same time, false-positive results per death averted would increase substantially. Adapting the age range of BC screening is an option to improve harm-to-benefit ratios in all four countries. Prioritization of considered harms and benefits affects the interpretation of results.

A convolutional neural network algorithm for breast tumor detection with magnetic detection electrical impedance tomography

Breast cancer is a malignant tumor disease for which early detection, diagnosis, and treatment are of paramount significance in prolonging the life of patients. Magnetic Detection Electrical Impedance Tomography (MDEIT) based on the Convolutional Neural Network (CNN), which aims to realize non-invasive, high resolution detection of breast tumors, is proposed. First, the MDEIT forward problem of the coronal and horizontal planes of the breast was simulated and solved using the Finite Element Method to obtain sample datasets of different lesions. Then, the CNN was built and trained to predict the conductivity distribution in different orientations of the breast model. Finally, noise and phantom experiments were performed in order to assess the anti-noise performance of the CNN algorithm and its feasibility of detecting breast tumors in practical applications. The simulation results showed that the reconstruction relative error with the CNN algorithm can be reduced to 10%, in comparison with the truncated singular value decomposition algorithm and back propagation algorithm. The CNN algorithm had better stability in the anti-noise performance test. When the noise of 60 dB was added, the shape of the breast tumor could still be restored by the CNN algorithm. The phantom experimental results showed that through the CNN based reconstruction algorithm, the reconstruction conductivity distribution image was legible and the position of the breast tumor could be determined. It is reasonable to conclude that the MDEIT reconstruction method proposed in this study has practical importance for the early and non-invasive detection of breast tumors.

Estimation of overdiagnosis by detection to incidence ratio in cancer screening

Objective

We aimed to introduce a concept of overdiagnosis with actual formulae. In screening for invasive cancer, the detection proportion to incidence rate (D/I) ratio is used as an intermediate indicator of effect. D is the detection rate (proportion) at screen and I is the background risk (i.e. the expected incidence rate if there were no screening). We sought to determine a proper use of the D/I ratio in the estimation of overdiagnosis in screening.

Methods

We propose the difference between the D/I ratio per year and incidence-based sensitivity as an estimate of overdiagnosis. As an example to evaluate this, we used screening for colorectal cancer, run as a randomized public health policy in Finland.

Conclusion

The use of the D/I ratio is inappropriate in predicting effect, and we recommend that the D/I ratio be used as a component in the estimation of overdiagnosis in screening for invasive cancer.

Too much medicine? Scientific and ethical issues from a comparison between two conflicting paradigms

BACKGROUND

The role of medicine in society appears to be focused on two views, which may be summarized as follows: "Doing more means doing better" (paradigm A) and "Doing more does not mean doing better" (paradigm B).

MAIN BODY

I compared paradigms A and B both in terms of a single clinical condition and in the general context of a medical system. For a single clinical condition, I analyzed breast cancer screening. There are at least seven interconnected issues that influence the conflict between paradigms A and B in the debate on breast cancer screening: disconnection between research and practice; scarcity of information given to women; how "political correctness" can influence the choice of a health policy; professional interests; doubts about effectiveness; incommensurability between harms and benefits; and the difficulty in making dichotomous decisions with discrete variables. As a general approach to medicine, the main representative of paradigm A is systems medicine. As representatives of paradigm B, I identified the following approaches or movements: choosing wisely; watchful waiting; the Too Much Medicine campaign; slow medicine; complaints against overdiagnosis; and quaternary prevention. I showed that both as a single condition and as a general approach to medicine, the comparison was entirely reducible to a harm-benefit analysis; moreover, in both cases, the two paradigms are in many respects incommensurable. This transfers the debate to the ethical level; consequently, scientists and the public have equal rights and competence to debate on this subject. Moreover, systems medicine has many ethical problems that could limit its spread.

CONCLUSION

I made some hypotheses about scenarios for the future of medicine. I particularly focused on whether systems medicine would become increasingly accessible and widespread in the population or whether it would be downsized because its promises have not been maintained or ethical problems will become unsustainable.

Fake facts and alternative truths in medical research

Background

Fake news and alternative facts have become commonplace in these so-called “post-factual times.” What about medical research - are scientific facts fake as well? Many recent disclosures have fueled the claim that scientific facts are suspect and that science is in crisis. Scientists appear to engage in facting interests instead of revealing interesting facts. This can be observed in terms of what has been called polarised research, where some researchers continuously publish positive results while others publish negative results on the same issue – even when based on the same data. In order to identify and address this challenge, the objective of this study is to investigate how polarised research produce “polarised facts.” Mammography screening for breast cancer is applied as an example.

Main body

The main benefit with mammography screening is the reduced breast cancer mortality, while the main harm is overdiagnosis and subsequent overtreatment. Accordingly, the Overdiagnosis to Mortality Reduction Ratio (OMRR) is an estimate of the risk-benefit-ratio for mammography screening. As there are intense interests involved as well as strong opinions in debates on mammography screening, one could expect polarisation in published results on OMRR. A literature search identifies 8 studies publishing results for OMRR and reveals that OMRR varies 25-fold, from 0.4 to 10. Two experts in polarised research were asked to rank the attitudes of the corresponding authors to mammography screening of the identified publications. The results show a strong correlation between the OMRR and the authors’ attitudes to screening (R = 0.9).

Conclusion

Mammography screening for breast cancer appears as an exemplary field of strongly polarised research. This is but one example of how scientists’ strong professional interests can polarise research. Instead of revealing interesting facts researchers may come to fact interests. In order to avoid this and sustain trust in science, researchers should disclose professional and not only financial interests when submitting and publishing research.

Electronic supplementary material

The online version of this article (10.1186/s12910-018-0243-z) contains supplementary material, which is available to authorized users.

Benefit-to-harm ratio of the Danish breast cancer screening programme

The primary aim of breast cancer screening is to reduce breast cancer mortality, but screening also has negative side‐effects as overdiagnosis. To evaluate a screening programme, both benefits and harms should be considered. Published estimates of the benefit‐to‐harm ratio, the number of breast cancer deaths prevented divided by the number of overdiagnosed breast cancer cases, varied considerably. The objective of the study was to estimate the benefit‐to‐harm ratio of breast cancer screening in Denmark. The numbers of breast cancer deaths prevented and overdiagnosed cases [invasive and ductal carcinoma in situ (DCIS)] were estimated per 1,000 women aged 50–79, using national published estimates for breast cancer mortality and overdiagnosis, and national incidence and mortality rates. Estimations were made for both invited and screened women. Among 1,000 women invited to screening from age 50 to age 69 and followed until age 79, we estimated that 5.4 breast cancer deaths would be prevented and 2.1 cases overdiagnosed, under the observed scenario in Denmark of a breast cancer mortality reduction of 23.4% and 2.3% of the breast cancer cases being overdiagnosed. The estimated benefit‐to‐harm ratio was 2.6 for invited women and 2.5 for screened women. Hence, 2–3 women would be prevented from dying from breast cancer for every woman overdiagnosed with invasive breast cancer or DCIS. The difference between the previous published ratios and 2.6 for Denmark is probably more a reflection of the accuracy of the underlying estimates than of the actual screening programmes. Therefore, benefit‐to‐harm ratios should be used cautiously.

What's new?

Breast cancer screening reduces breast cancer mortality, but one negative side‐effect is overdiagnosis. Published estimates of the benefit‐to‐harm ratio–the number of prevented breast cancer deaths divided by the number of overdiagnosed breast cancer cases–vary considerably. This study reports a benefit‐to‐harm ratio of 2.6 for women invited to breast cancer screening in Denmark. Among 1,000 invited women from age 50 and followed up until 79, 2–3 women would be prevented from dying from breast cancer for every overdiagnosed woman. International variations in benefit‐to‐harm ratios probably reflect differences in the accuracy of underlying estimates more than differences between screening programmes.