Table 2 Baseline characteristics of study population matched by age, date of mammogram, and study

N

1171

1659

Mean age at mammogram (years)

55.4 (10.6)

55.3 (10.6)

Mean age at diagnosis (years)

60.5 (10.8)

–

Mean BMI (kg/m²)

25.7 (6.1)

25.8 (6.8)

  < 25

551 (47.1%)

854 (51.5%)

 25–29

369 (31.5%)

443 (26.7%)

 30–34

155 (13.2%)

196 (11.8%)

 35+

73 (6.2%)

136 (8.2%)

 Unknown

23 (2.0%)

30 (1.8%)

 Premenopausal

430 (36.7%)

632 (38.1%)

 Postmenopausal

697 (59.5%)

962 (58%)

 Unknown

44 (3.8%)

65 (3.9%)

 Nulliparous

169 (14.4%)

218 (13.1%)

 Parous

977 (83.4%)

1415 (85.3%)

 Unknown

25 (2.1%)

26 (1.6%)

Postmenopausal hormone therapy^a*

 Not current

255 (51.5%)

367 (57.5%)

 Current, estrogen

116 (23.4%)

156 (24.5%)

 Current, estrogen + progestin

124 (25.1%)

115 (18.0%)

 No

973 (83.1%)

1453 (87.6%)

 Yes

196 (16.7%)

206 (12.4%)

 Unknown

2 (0.2%)

0 (0%)

Standardized mean percent mammographic density (%)*

32.9 (18.7)

27.9 (18.4)

Standardized mean dense area (cm²)*

63.5 (43.1)

52.2 (37.8)

Standardized mean non-dense area (cm²)*

149.4 (98.7)

158.9 (102.1)