Table 1.

Baseline characteristics by study arm

AspirinPlaceboAll participants
N = 76N = 68N = 144
Mean (SD)Mean (SD)P (t test)Mean (SD)
Age59.9 (5.5)59.1 (5.4)0.3859.4 (5.4)
Age at menopause, y49.6 (6.4)50.1 (5.4)0.5149.9 (5.9)
Years since menopause9.7 (8.0)8.8 (7.7)0.249.6 (8.1)
BMI, kg/m226.8 (6.1)25.9 (4.1)0.2826.4 (5.4)
Number of pregnancies >6 mo1.68 (1.84)1.65 (1.30)0.531.66 (1.57)
N (%)N (%)P (χ2 test)N (%)
Race/ethnicity
 Non-Hispanic White70 (92.1)65 (95.6)0.21135 (93.7)
 Other6 (7.9)3 (4.4)9 (6.3)
Education
 High school or less2 (2.6)2 (2.9)0.874 (2.8)
 Some college/vocational17 (22.4)16 (23.5)33 (22.9)
 College degree28 (36.8)23 (33.8)60 (41.7)
 Postgraduate29 (38.2)27 (39.7)56 (38.9)
Family history of breast cancer
 Yes18 (23.6)18 (26.9)0.4136 (25)
 Missing1 (1.3)1 (1.5)2 (1.4)
BI-RADS mammogram density
 Class 27 (9.2)7 (10.3)14 (9.7)
 Class 340 (52.6)39 (57.4)0.7479 (54.9)
 Class 427 (35.5)22 (32.3)49 (34.0)
 Missing2 (2.6)02 (1.4)
Previous breast biopsy
 Yes16 (21.1)20 (29.4)0.2336 (25.0)
 Don't know202 (1.4)
Bilateral oophorectomy
 Yes7 (9.2)7 (10.3)0.3514 (9.7)
 Don't know101 (0.7)
Hysterectomy
 Yes16 (21.1)12 (17.7)0.6128 (19.4)
Past menopausal estrogen use
 Yes46 (60.5)38 (55.9)0.6484 (58.3)
 Missing011 (0.7)
Geometric mean (95% CI)Geometric mean (95% CI)Geometric mean (95% CI)
Estrone, pg/mL31.1 (29.0–33.3)33.4 (30.8–36.2)0.2032.2 (30.5–33.9)
Estradiol, pg/mL7.2 (6.5–8.1)7.6 (6.8–8.4)0.567.4 (0.69–8.0)
Free estradiol, pg/mL0.177 (0.16–0.20)0.180 (0.16–0.20)0.560.178 (0.164–0.194)
Bioavailable estradiol, pg/mL4.53 (4.01–5.11)4.56 (4.04–5.15)0.944.54 (4.17–4.95)
SHBG, nmol/L45.8 (41.5–50.7)51.1 (46.3–56.3)0.1348.2 (45.0–51.8)