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Harms and Benefits of Mammographic Screening for Breast Cancer in Brazil

Arn Migowski, Paulo Nadanovsky, Cid Manso de Mello Vianna

Abstract

In the absence of evidence on the effect of mammographic screening on overall mortality, comparing the number of deaths avoided with the number of deaths caused by screening would be ideal, but the only existing models of this type adopt a very narrow definition of harms. The objective of the present study was to estimate the number of deaths prevented and induced by various mammography screening protocols in Brazil.

Introduction

In the absence of evidence on the impact of mammographic screening on overall mortality, many attempts to determine the balance between the harms and benefits of screening compare different outcomes, generating a search for an arbitrary and questionable ideal balance value between these outcomes [1]. These comparisons make it difficult for physicians and women to decide on screening because the benefits are usually expressed by a more severe outcome (mortality from breast cancer) and the harms are expressed by intermediate outcomes that are difficult to understand and less severe, such as false-positive results and rate of overdiagnosis [2]. As a result, these intermediate harm outcomes are generally not as valued by women as the possible benefits [3] and can even be interpreted as a benefit [2].

Materials and method

A simulation study was conducted based on life tables, using secondary national-level demographic, breast cancer screening and multiple-cause mortality data, all available without any identifiable information and freely accessible on the website of the Brazilian Ministry of Health, which is responsible for storing data from various official sources of information in the country. The harm and benefit parameters were obtained through systematic literature searches performed by the authors and have already been described in detail elsewhere [11–13]. S1-S3 Tables in S1 File present a summary of the main data sources that were used for all outcomes included in the simulations to evaluate the potentially lethal harms and benefits of mammographic screening.

Results

Even in the unlikely event that screening from 40 to 49 years was found to be efficacious (best scenario), the NNS would be much higher, with an ARR value almost 10 times lower than in the best scenario for biennial screening from 50 to 69 years (Table 1). The superiority of the absolute benefit of screening in the age group of 60 to 69 years is evident in the number of deaths from breast cancer avoided in the screening, being almost three times higher than that for the age group of 50 to 59 years in the base case (Table 1). The comparison of the results found for screening benefits in Brazil with other results in the literature are described in S8 and S9 Tables in S1 File.

Discussion

To the best of our knowledge, this is the broadest study on harm estimation of breast cancer screening ever published, evaluating the absolute impact of mammographic screening not only in terms of deaths avoided but also considering a broad spectrum of deaths caused by screening. It is common, for example, for deaths from breast cancer induced by radiation from screening mammograms to be considered the only cause of death attributed to screening, in most cases excluding even ionizing radiation associated with false-positive cases, assuming in a biased manner that the benefits outweigh the harms [4, 17, 18, 30]. Even other models that consider other types of screening risks [7, 16] are less comprehensive than the present study in terms of harms of screening. The same occurs in systematic reviews and clinical guidelines [11, 20, 31, 32].

Conclusions

The present study indicates that the benefits of mammographic screening in terms of deaths avoided by screening outweigh its harms in terms of deaths caused by screening in biennial screening from 50 to 59 years, 60 to 69 years and 50 to 69 years. None of the sensitivity analyses altered this conclusion for these screening protocols. However, even in this age group, the estimated effect for Brazil in reducing breast cancer mortality was half that estimated for the United Kingdom, for instance, even assuming the same RR. Although false-positives and cases of overdiagnosis are more frequent than both deaths caused and prevented by screening, our results offer an additional and more direct comparision between benefits and harms.

Citation: Migowski A, Nadanovsky P, Manso de Mello Vianna C (2024) Harms and benefits of mammographic screening for breast cancer in Brazil. PLoS ONE 19(1): e0297048. https://doi.org/10.1371/journal.pone.0297048

Editor: Daniele Ugo Tari, Local Health Authority Caserta: Azienda Sanitaria Locale Caserta, ITALY

Received: April 4, 2023; Accepted: December 26, 2023; Published: January 25, 2024

Copyright: © 2024 Migowski et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Mortality Data: DATASUS website: https://datasus.saude.gov.br/transferencia-de-arquivos/ and at: http://tabnet.datasus.gov.br/cgi/deftohtm.exe?sim/cnv/obt10uf.def Population Data (IBGE): https://datasus.saude.gov.br/transferencia-de-arquivos/ and at: https://datasus.saude.gov.br/populacao-residente.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Source: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0297048#sec010

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