Interval breast cancers in the NHS Breast Screening Programme: does the current definition exclude too many?

Area of Science:

• Oncology
• Public Health
• Radiology

Background:

• Interval breast cancers are detected between routine screening rounds.
• Accurate measurement of interval cancer rates is crucial for evaluating screening program effectiveness.
• The definition of interval cancers can influence observed rates.

Purpose of the Study:

• To assess how different definitions of interval breast cancers affect the calculated rates from the initial screening round.
• To investigate the impact of exclusion criteria, particularly those used in national statistics, on interval cancer rates.

Main Methods:

• Identified interval breast cancers from the prevalent screening round at a specific UK breast screening unit.
• Applied standard exclusion criteria used in national statistics to quantify their effect.
• Determined individual screening round lengths for women with incident cancers.

Main Results:

• A total of 278 interval cancers were identified, yielding an overall rate of 47.1/10,000 women.
• Applying national exclusion criteria reduced the rate to 36.1/10,000 ('core' interval cancers), a 23.4% decrease.
• Excluding cancers diagnosed 36 months or later post-screening caused the largest reduction.

Conclusions:

• The criteria used to define interval breast cancers substantially alter observed rates.
• Excluding cancers diagnosed 36 months or more after the last screen may obscure important data for the NHSBSP.
• Revisiting exclusion criteria is necessary to ensure accurate monitoring of breast screening program performance.