Table 3.

Percent Breast Cancer Mortality Reduction Maintained when Moving from an Annual Screening Interval to a Biennial Interval by Screening Strategy and Model

Model	Percent Mortality Reduction Maintained by Screening Strategy
	50–69	40–69	45–69	40–79	40–84	55–69	60–69	50–74	50–79	50–84
D	76%	75%	78%	79%	82%	83%	79%	81%	78%	83%
E	75	73	74	75	75	75	73	76	75	76
G	85	86	91	87	88	91	86	89	88	89
M	90	96	97	97	99	92	84	95	93	95
S	74	73	78	76	77	80	74	79	85	79
W	68	67	70	70	71	71	70	72	70	73

Model Group Abbreviations: D (Dana Farber Cancer Center), E (Erasmus Medical Center), G (Georgetown U.), M (M.D. Anderson Cancer Center), S (Stanford U.), W (U. of Wisconsin/Harvard)

Differences in the range of results reflect differences in modeling approaches. For example, the benefit of screening in model M is modeled through stage shift, as with most other models, but also includes a “beyond stage shift” factor based on a cure fraction for small tumors. However, since many of these “cures” occur among women with invasive cancers that are not lethal, finding such cancers a year earlier confers very little mortality advantage to annual (vs. biennial) screening.