Table 2. Benefits and harms of breast cancer screening by different ages for initiating and terminating screening.

Strategy	Screenings, womena	Benefit					Harm
		Number of deathsa	Reduced number of deaths	Death reduction, %	Maintained death reduction, %b	Extended average life expectancy, dayc	False-positive resultsa	Number need to screen to detect one diagnosis	Number need to screen to avert one death
Japan
Biennial screening
No breast cancer	—	—	—	—	—	—	—	—	—
No screening	—	2657	—	—	—	—	—	—	—
40–69 y	1 443 763	1821	836	31	80	58	105 162	218	793
50–69 y	947 159	1952	705	27	81	45	57 470	149	485
40–74 y	1 704 723	1695	962	36	83	62	120 820	239	1006
50–74 y	1 208 118	1825	832	31	84	49	73 127	176	662
40–79 y	1 867 271	1636	1021	38	82	63	130 573	251	1141
50–79 y	1 370 666	1764	893	34	83	51	82 880	191	777
Annual screening
40–69 y	2 877 439	1612	1045	39	—	72	209 656	407	1785
50–69 y	1 885 811	1787	870	33	—	55	114 430	278	1055
40–74 y	3 311 710	1491	1166	44	—	76	235 712	439	2221
50–74 y	2 320 081	1665	992	37	—	59	140 486	320	1393
40–79 y	3 717 061	1406	1251	47	—	78	260 033	466	2644
50–79 y	2 725 432	1582	1075	40	—	61	164 807	355	1723
United States
Biennial screening
No breast cancer	—	—	—	—	—	—	—	—	—
No screening	—	9238	—	—	—	—	—	—	—
40–69 y	1 401 446	6926	2312	25	74	137	123 917	119	202
50–69 y	906 670	7202	2036	22	74	112	75 422	80	126
40–74 y	1 627 584	6260	2978	32	78	157	139 521	118	260
50–74 y	1 132 808	6536	2702	29	79	132	91 025	85	173
40–79 y	1 757 771	5902	3336	36	76	164	148 504	117	298
50–79 y	1 262 995	6180	3058	33	77	139	100 008	87	204
Annual screening
40–69 y	2 784 694	6098	3140	34	—	183	246 301	210	457
50–69 y	1 797 511	6496	2742	30	—	147	149 544	142	277
40–74 y	3 159 597	5403	3835	42	—	203	272 169	208	585
50–74 y	2 172 414	5801	3437	37	—	167	175 412	149	374
40–79 y	3 482 743	4856	4382	47	—	214	294 466	205	717
50–79 y	2 495 560	5253	3985	43	—	178	197 709	152	475

^aScreenings, number of deaths, and false-positive results are all represented as the sum total (60-year follow-up from age 40). Death reduction and average life expectancy extension were compared between 100% screened and unscreened women. Mortality rate of women with undetected breast cancer is 1.5 times that of women with detected breast cancer.
^bTo examine the effect of screening intervals, the ratio of biennial-to-annual benefit were calculated (with the proportion of death reduction maintained).
^cThe theoretical maximal benefits of screening were 157 days (88.15 − 87.72 = 0.43 years) and 408 days (83.03 − 81.91 = 1.12 years) in Japan and the United States.