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Grand Rounds

How Effective Is Mammography in Reducing the Number of Advanced Breast Cancer Diagnoses?

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BACKGROUND AND PURPOSE:

  • The goal of cancer screening programs is to reduce cancer mortality by decreasing the number of individuals who present for cancer care with advanced disease
  • In 1988, the Netherlands adopted a population based breast cancer screening program
  • Follow-up studies indicated deaths from breast cancer declined following 1995
    • From 1989–1997, there was decline in the incidence of tumors ≥ 20 mm with positive nodes and/or metastases in women between 50-69 years of age
    • Tumors <20 mm with metastases or tumors ≥ 20 mm but no metastases were unchanged
  • Autier et al. (BMJ, 2017) updated the above data and analyzed the change in rates of stage specific incidence of breast cancer and breast cancer mortality from 1989-2012

METHODS:

  • Population based study
    • 1989-1996: Women age 50-69 offered biennial mammography
    • 1997: Women age 70-75 were also offered biennial mammography
    • 2006: Digital mammography replaces film based mammography
    • Approximately 80% of women opted for screening, mostly between ages 50-75
  • Threshold diameter between stage 1 and stage 2 is 20 mm
    • Early cancer: Stage 1 and in-situ
    • Advanced cancer: Stage 2-4
    • Survival in stage 1 is closer to women without breast cancer, while stages 2-4 are associated with reduced survival
  • Overdiagnosis was defined as the incidence of in situ and stage 1 breast cancer in excess to the incidence that would be expected in the absence of screening, adjusting for clinical lead time
  • Basic assumptions from the literature
    • Out of 3 stage 1 tumors detected by screening that would have been diagnosed at stage 2-4 without, two deaths from breast cancer would be prevented (3:2 ratio)
  • Breast cancer mortality reductions during 2010-12 and overdiagnosis during 2009-2011 were computed without (scenario 1) and with (scenario 2) a cohort effect on mortality
    • Cohort effect is independent of screening
    • Investigators have identified a gradual decrease in lifetime risk of breast cancer death based on birth cohort and adjusted for this in scenario 2

RESULTS:

  • In 1989, the incidence of stage 2-4 breast cancer in women was 168/100,000 and decreased negligibly to 166/100,000 by 2012
  • The incidence of in situ and stage 1 cancers increased
    • For ages 50-69, there was sharp increases in incidence in 1990-1996, with further increases to 2007, and then another sharp increase with the introduction of digital mammography
  • Screening in women ≥50 years was associated with
    • 5% mortality reduction in scenario 1
    • No change in scenario 2 (adjusted for cohort effects)
      • Cohort effect independently reduced mortality by 5%
    • Regardless of cohort effect, improved treatments would result in a 28% breast cancer mortality reduction
    • Timing and magnitude of decreases in mortality were similar among women <50 years (not in the screening program) and those age 50-69

CONCLUSION:

  • Authors acknowledge limitations
    • Due to the high rate of screening uptake, they do not have a direct, contemporaneous cohort without screening to serve as controls for comparison
  • The results of this study demonstrates that the Dutch mammography screening program has had little impact on the burden of advanced breast cancers
    • Therefore, one can assume only a marginal effect on breast cancer mortality
  • Overdiagnosis has steadily increased over time and increasing with opening up the program to older women and using advanced digital technologies
  • As of 2012, about half of screen detected breast cancers represent overdiagnosis
  • The authors calculate that for one woman who would not die from breast cancer, 14 women would be overdiagnosed with an in situ or stage 1 cancer
    • Using scenario 2 and correcting for cohort effect, there would be no additional early detection of cancers that would be stage 2-4 without the screening program

Learn More – Primary Sources:

Effectiveness of and overdiagnosis from mammography screening in the Netherlands: population based study

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Related ObG Topics:

Has Breast Density Legislation Had Any Impact on Breast Cancer Diagnosis? 
Discussing Sexual Health: Medical Considerations and Recommendations
Which Mammography Recommendation Results in the Greatest Breast Cancer Mortality Reduction?
Professional Recommendations for Use Pharmacologic Interventions to Reduce Breast Cancer Risk

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