The incidence and 10-year survival of interval breast cancers in Wales

To evaluate the number of interval cancers (IC) within one screening cycle and the overall 10-year survival of IC, including its four main classifications, and compare that to screen-detected cancers (SDC).

Within Breast Test Wales (BTW), all SDC between the years 1998 and 2001 were included. IC that occurred between 1998 and 2003 that had undergone screening between the years 1998 and 2001 were also included. These IC were classified into true interval (TI), false negative (FN), occult cancer (OCC), and unclassified cancer (UCC). BTW received notification of all deaths of women that had undergone screening; thus, the 10-year all-cause survival rate was calculated from the date of diagnosis and death.

During the study period, 199,082 women attended screening. Of these, 1020 (0.51%) women had SDC and 692 (0.38%) women developed IC. Of the 692 IC, 391 (57.8%) were TI, 120 (17.7%) were FN, 68 (10%) were OCC, and 98 (14.5%) were UCC; 15 (2.2%) were not classified. After a 10-year follow-up period, the 10-year survival rate (all-cause) for SDC was 81.6%, overall for all of IC was 72.4% (OR = 1.67, p < 0.001), TI was 77.5% (OR = 1.00, p = 0.99), FN was 55% (OR = 2.36, p < 0.001), OCC was 54.4% (OR = 3.17, p < 0.001), and UCC was 87.8% (OR = 0.61, p = 0.19).

The overall 10-year survival of IC was significantly different to SDC. However, within this, the prognosis of TI was similar to SDC, whereas FN and OCC had significantly worse long-term survival. Further research is required to identify the underlying cause of poor survival of FN and OCC.