Table 2:

Estimated proportion of breast cancers overdiagnosed from screening^* (15)

Age of women at initial screen, yr	Years after screening	Breast cancers estimated as overdiagnosed, %
Age of women at initial screen, yr	Years after screening	Invasive and in situ cancers, %	Invasive cancers, %
40 to 49	5	41	32
	20	55	48
50 to 59	5	25	16
	20	16	5

↵* Overdiagnosis by age was estimated using this calculation: The numerator is the difference in numbers of cancers in the mammography arm less those in the control arm; and the denominator is the number of screen-detected cancers in the mammography arm. (39) Only the findings from the estimate on overdiagnosis from a Canadian randomized controlled trial (39) are included because it provided an estimate by age and was appraised as being at moderate risk of bias. (15)