Flawed assumptions used to defend screening mammography

The current status of risk-stratified breast screening

Apart from high-risk scenarios such as the presence of highly penetrant genetic mutations, breast screening typically comprises mammography or tomosynthesis strategies defined by age. However, age-based screening ignores the range of breast cancer risks that individual women may possess and is antithetical to the ambitions of personalised early detection. Whilst screening mammography reduces breast cancer mortality, this is at the risk of potentially significant harms including overdiagnosis with overtreatment, and psychological morbidity associated with false positives. In risk-stratified screening, individualised risk assessment may inform screening intensity/interval, starting age, imaging modality used, or even decisions not to screen. However, clear evidence for its benefits and harms needs to be established. In this scoping review, the authors summarise the established and emerging evidence regarding several critical dependencies for successful risk-stratified breast screening: risk prediction model performance, epidemiological studies, retrospective clinical evaluations, health economic evaluations and qualitative research on feasibility and acceptability. Family history, breast density or reproductive factors are not on their own suitable for precisely estimating risk and risk prediction models increasingly incorporate combinations of demographic, clinical, genetic and imaging-related parameters. Clinical evaluations of risk-stratified screening are currently limited. Epidemiological evidence is sparse, and randomised trials only began in recent years.

Effect of organised mammography screening on stage-specific incidence in Norway: population study

Background:

We aimed to estimate the effect of organised mammography screening on breast cancer stage distribution by comparing changes in women eligible for screening, based on birth cohort, to the concurrent changes in younger, ineligible women.

Methods:

In an open cohort study in Norway, which introduced national mammography screening county-by-county from 1995 to 2004, we identified women (n=49 883) diagnosed with in situ or invasive breast cancer (ICD10 codes: D05 or C50) during the period 1987–2011 and born between 1917 and 1980. We estimated relative incidence rate ratios (rIRRs) comparing the development in the screening vs historic group to the younger vs younger historic group.

Results:

Including the compensatory drop, eligible women experienced a 68% higher increase in localised cancers (rIRR=1.68, 95% confidence interval (CI): 1.51–1.87) than younger women, while the increase in incidence of advanced cancers was similar (rIRR=1.11, 95% CI: 0.90–1.36). Excluding the prevalence round, eligible women experienced a 60% higher increase in localised cancers (rIRR=1.60, 95% CI: 1.42–1.79), while the increase in incidence of advanced cancers remained similar (rIRR=1.08, 95% CI: 0.86–1.35).

Conclusions:

Introduction of organised mammography screening was followed by a significant increase in localised and no change in advanced-stage cancers in women eligible for screening relative to younger, ineligible women.

Screening mammography: update and review of publications since our report in the New England Journal of Medicine on the magnitude of the problem in the United States

RATIONALE AND OBJECTIVES

After a half century of clinical trials, expansive observations, vigorous advocacy and debate, screening mammography could not be in a more controversial condition, especially the potential harm of overdiagnosis. Despite a simple rationale (catch the cancer early and either prevent death or at least decrease the amount of therapy needed for cure), the estimates to date of overdiagnosis rates are conflicting and the interpretations complex.

MATERIALS AND METHODS

Since the author's 2012 publication in the New England Journal of Medicine (NEJM), the peer-reviewed publications on overdiagnosis caused by screening mammography are reviewed and the NEJM analyses updated with three additional calendar years of results.

RESULTS

The recent peer-reviewed medical literature on screening mammography induced overdiagnosis of breast cancer has increased exponentially, nearly 10-fold in 10 years. The average estimate of overdiagnosis is about 30%, but the range extends from 0% to 70+%. An update of the NEJM report estimates that in the US, 78,000 women and 30%-31% of those diagnosed with breast cancer at the age of 40 years or older during 2011 were overdiagnosed.

CONCLUSIONS

Until we have better screening procedures that identify who really has cancer and needs to be treated, the risk of overdiagnosis relative to the benefit of screening merits more effective public and professional education. Radiologists, pathologists, and other professionals involved with screening mammography should recognize that the potential harm of overdiagnosis is downplayed or not discussed with the patient and family, despite agreement that the objective is informed choice.

At what age should screening mammography be recommended for Asian women?

Although regular screening mammography has been suggested to be associated with improvements in the relative survival of breast cancer in recent years, the appropriate age to start screening mammography remains controversial. In November 2009, the United States Preventive Service Task Force published updated guidelines for breast cancer, which no longer support routine screening mammography for women aged 40–49 years, but instead, defer the choice of screening in that age group to the patient and physician. The age to begin screening differs between guidelines, including those from the Task Force, the American Cancer Society and the World Health Organization. It remains unclear how this discrepancy impacts patient survival, especially among certain subpopulations. Although the biological characteristics of breast cancer and peak age of incidence differ among different ethnic populations, there have been few reports that evaluate the starting age for screening mammography based on ethnicity. Here, we discuss the benefits and harm of screening mammography in the fifth decade, and re-evaluate the starting age for screening mammography taking ethnicity into account, focusing on the Asian population. Breast cancer incidence peaked in the fifth decade in Asian women, which has been thought to be due to a combination of biological and environmental factors. Previous reports suggest that Asian women in their 40s may receive more benefit and less harm from screening mammography than the age-matched non-Asian US population. Therefore, starting screening mammography at age 40 may be beneficial for women of Asian ethnicity in well-resourced countries, such as Japanese women who reside in Japan.