Breast screening

Section: Breast Curriculum: Curriculum, page 11

Reduces risk of Breast Ca death by 16%

Aim

• Reduce morbidity and mortality of breast cancer by detecting it early and treating when small
• WHO principles of population screening

Adverse effects

• Anxiety related to recall
• Open surgical biopsy sometimes performed for what turns out to be benign disease
• Overdiagnosis
  • E.g. Will low grade DCIS ever threaten this patient’s life?

Breastscreen Aotearoa

• 45-69yrs in NZ (since 1988)
• 2yrly Mamogram, MLO + CC
  • 2 views increases detection of small cancers by 42%
    • Ideal film density = 1.5-1.9
    • Double reading improves sensitivity by 5-10%
    • 98% sensitive in older population
• Clinical and self-exam don’t decrease mortality

Findings

• Well defined mass
  • Almost always benign, PPV <1% for Ca
• Ill-defined mass
  • Always requires further assessment, PPV 35-50%
• Spiculated mass
  • PPV 50-90%
• Clustered microcalcifications
  • PPV 15% for Ca
  • Account for high amount of recalls
  • Most common way to pick up DCIS

BI-RADS assessment categories

BI-RADS breast density

Targets

• Open Bx ≤ 1%
• Aim for 90% of benign specimens < 30g
• Interval malignancy rates
  • < 0.6/1000 1st year
  • < 1.2/1000 2nd year
• Screen detected Ca: Node -ve: ≥ 70% Size ≤ 14mm
• Recall rate < 7%
• 80% of these benign
• For every 10,000 screened – 27-30 invasive ca, 5-10 DCIS
• 55% < 15mm

Factors affecting the effectiveness of screening

• HRT or implants
• Increases breast density, reduces mammography sensitivity

Most important screen detected cancers

• High grade DCIS
  • Will progress to G2/3 invasive ca within 3yrs
• Grade 2 + 3 tumours

Breast Screening Evidence

• Mortality
  • 15-20% reduction in women 40-69
    • Mortality ↓ not observed in 40-49yr group
      • 20% of breast Ca are diagnosed in women in their 40s (screening benefits unclear)
  • But also 30% ↑ risk (≈ 0.5% absolute risk) of over diagnosis / overtreatmen
• Overall
  • For every 2000 women screened over 10yrs
    • ONE will have her life prolonged
    • 10 healthy women will incorrectly be diagnosed as “Breast Ca” and treated unnecessarily
• 25% decrease in rate of stage II / advanced CA
• False -ves:
  • ~ 10% of cancers are missed by mammography in women aged 50-59
  • 25% are missed in women 40-49
• Radiation risk
  • Estimate for screening between 50-64 causing cancer is approx. 1/20,000 <0.4 cGy per view