Interval breast cancer (a cancer found between screening rounds)

The NHS Breast Screening Programme invites everyone registered as female with a GP from age 50 (first invitation between 50 and 53) every three years until the 71st birthday, and women 71 or over can request screening; anyone worried about symptoms should see a GP even if recently screened rather than wait for the next appointment (NHS). An interval cancer emerges after a negative screen. In population programmes, most based on two-yearly screening, reported interval cancer rates ranged from 7.0 to 49.3 per 10,000 screens, usually 8.4 to 21.1 per 10,000 across the two-year interval with the larger share in the second year; on retrospective review most interval cancers were true interval or occult cancers not visible on the index mammogram and about 20 to 25 percent were classified as missed; interval cancers have worse prognostic characteristics, biomarker profiles and survival than screen-detected cancers but resemble cancers in unscreened women (Houssami 2017). Triple-negative disease is over-represented: in 15,204 women at US NCCN centres only 29 percent of triple-negative cancers presented through an abnormal screening mammogram against 48 percent of hormone receptor-positive, HER2-negative cancers (Lin 2012), and triple-negative tumours are diagnosed younger, before the screening age in many cases (Bauer 2007; Scott 2019). Women at high familial risk are screened differently: NICE CG164 offers annual MRI from 30 to 49 and annual mammography from 40 to 69 to known BRCA1 or BRCA2 carriers, and in the UK MARIBS study MRI detected 77 percent of cancers against 40 percent for mammography, 92 against 23 percent in BRCA1 carriers, with two interval cases among 35 cancers in 1,881 screens (Leach 2005).