Interval cancers in the Dutch breast cancer screening programme

The nationwide breast cancer screening programme in The Netherlands for wom en aged 50-69 started in 1989. In our study we assessed the occurrence and stage distribution of interval cancers in women screened during 1990-1993. Records of 0.84 million screened women were linked to the regional cancer r egistries yielding a follow-up of at least 2.5 years. Age-adjusted incidenc e rates and relative (proportionate) incidences per tumour size including d uctal carcinoma in-situ were calculated for screen-detected and interval ca ncers, and cancers in not (yet) screened women, comparing them with publish ed data from the UK regions North West and East Anglia. In total 1527 inter val cancers were identified: 0.95 and 0.99 per 1000 woman-years of follow-u p in the 2-year interval after initial and subsequent screens respectively in the first year after initial screening interval cancers amounted to 27% (26% after subsequent screens) of underlying incidence, and in the second y ear to 52% (55%). Generally, interval cancers had a more favourable tumour size distribution than breast cancer in not (yet) screened women. The Dutch programme detected relatively less (favourable) invasive cancers in initia l screens than the UK programme, whereas the number of interval cancers con firms UK findings. Measures should be considered to improve the detection o f small invasive cancers and to reduce false-negative rates, even if this w ill lead to increasing referral rates. (C) 1999 Cancer Research Campaign.