Table 2.

Screening mammograms: cancer rate by family history of breast cancer in first-degree relatives and by age group^*

Family history of breast cancer in first-degree relatives and age group	Screening mammograms, No. (%)	Cancers, No. (%)	Cancer detection rate, No. of cancers per 1000 mammograms (95% CI)
Total	86 781 (100.0)	144 (100.0)	1.7 (1.4 to 1.9)
Age 18–34 y	13446	26	1.9 (1.3 to 2.8)
Yes	3548 (26.4)	3 (11.5)	0.8 (0.2 to 2.2)
No	8302 (61.7)	18 (69.2)	2.2 (1.3 to 3.3)
Missing†	1596 (11.9)	5 (19.2)	3.1 (1.1 to 6.7)
Age 35–39 y	73335	118	1.6 (1.3 to 1.9)
Yes	5933 (8.1)	9 (7.6)	1.5 (0.7 to 2.7)
No	59 166 (80.7)	94 (79.7)	1.6 (1.3 to 1.9)
Missing†	8236 (11.2)	15 (12.7)	1.8 (1.0 to 2.9)

^*CI = confidence interval.

^†In some practices, the categories “no” and “missing” were not separated. When we combined the missing and no categories, the percent cancer rate was 0.8% for a positive family history and 3.0% for a no or missing family history.