Table. Interval cancers (in situ plus invasive) at initial screening as part of the mammography screening program, 2005 to 2008.

Region	Negative results at initial screening	Interval cancers, 1 to 12 months: n (per 10 000)	Interval cancers, 13 to 24 months: n (per 10 000)	Background incidence rate (invasive only) per 10 000	Relative interval cancer rate* : 1st year/2nd year
WL	475 082	371 (7.8)	792 (16.7)	26.9	0.29/0.62
NO	403 682	282 (7.0)	591 (14.6)	26.9	0.26/0.54
NRW	878 764	653 (7.4)	1383 (15.7)	26.9	0.27/0.58

WL = Westphalia–Lippe; NO = North Rhine; NRW = North Rhine–Westphalia; ^*[interval cancer/background incidence rate]