Interval cancers in a French breast cancer-screening programme (Somme Department)

The objective of this study is to analyse the detection rates and tumour diameter of interval cancers in the breast cancer mass-screening programme of Somme Department (France), launched in 1990. Interval cancers are defined as breast cancers diagnosed within 36 months after a negative screening assessment, for women attending the programme between December 1990 to December 1993. Age-adjusted incidence rates were 0.51 per 1000 woman-years of follow-up in the 3-year interval after initial and subsequent screens. Diagnosis is made at early stage (sizes < or = 10 mm) in 20% of interval cancers. This stage is higher than that in screened women (9% of in situ cases and 35% of very small tumours). Interval cancer rates are low during the first year (0.18 per 1000 woman-years of follow-up) but higher in the second and third years.