Table 1 Descriptive statistics comparing screen-detected cancers and interval cancers

Mean age at mammography (yr)

62.0

60.9

0.012

Mean BMI

26.1

25.2

<0.001

Mean age at menarche (yr)

13.5

13.5

0.442

Oral contraceptive use, n (%)

0.003

   Yes

358 (32%)

118 (42%)

   No

754 (68%)

165 (58%)

Mean age at first birth (yr)

25.4

25.0

0.172

Mean parity (n)

1.8

1.9

0.775

Breastfeeding, n (%)

0.152

   Yes

777 (78%)

211 (82%)

   No

219 (22%)

46 (18%)

Mean age at menopause (yr)

50.4

50.2

0.302

HRT use, n (%)

<0.001

   Never

800 (73%)

160 (57%)

   Past

247 (22%)

71 (25%)

   Current

54 (5%)

52 (18%)

Previous benign breast disease, n (%)

0.182

   Yes

146 (13%)

46 (16%)

   No

965 (87%)

238 (84%)

Breast cancer heredity^a, n (%)

0.434

   Yes

160 (15%)

46 (17%)

   No

923 (85%)

230 (83%)

Percentage density (PD), n (%)

<0.001

   <5%

240 (22%)

38 (13%)

   5% to <10%

207 (19%)

50 (18%)

   10% to <25%

420 (38%)

100 (35%)

   25% to <50%

214 (19%)

79 (28%)

   ≥50%

34 (3%)

18 (6%)