A comparative audit of prevalent, incident and interval cancers in the Avon breast screening programme.

The 4th year of the Avon breast screening programme comprises two distinct groups: those called for screening for the first time (prevalent group) and those who were initially screened 3 years earlier (incident group). The cancer detection rate, stage of disease and rate of interval cancers in these patients have been compared. For the prevalent groups of year 1 and year 4 there was no statistically significant difference in the cancer detection rate, proportion of small tumours or node positivity. For the prevalent and incident groups of year 4, there was no statistically significant difference in the cancer detection rate or proportion of small tumours. There were significantly fewer node-positive tumours in the incident group (5/45 vs 8/23; P < 0.05). Fifty-six interval cancers presented in the 3-year period between years 1 and 4 of screening; 28 (50%) after 24 months. The screening programme may result in tumours being detected at an earlier stage, but this may be offset by the high rate of interval cancers. This suggests that the time between screens may need to be reduced to 2 years.