Table 1.

Age-standardized characteristics of the study population at benign breast biopsy by breast cancer case-control status in the NHS and the NHSII

Controls (N = 233)Casesa (N = 69)
Stained for p27 expression in normal breast TDLUs
 Percentage of p27+, median (IQR)b15.4 (25.0)16.1 (26.0)
Stained for ER expression in normal breast TDLUs
 Percentage of ER+, median (IQR)b6.4 (12.0)5.0 (10.8)
Stained for Ki67 expression in normal breast TDLUs
 Percentage of Ki67+, median (IQR)b0.77 (2.5)1.15 (2.7)
Age, yearsb44.6 (8.8)43.5 (9.0)
Type of benign lesion
 - Nonproliferative, %28.223.1
 - Proliferative without atypia, %55.749.9
 - Proliferative with atypical hyperplasia, %16.127.0
Height, inches64.6 (2.7)64.3 (2.1)
Average body size at ages 5–10 years
 - Level 1 (most lean), %32.332.0
 - Level 1.5–2, %30.135.9
 - Level 2.5–3, %16.39.2
 - Level 3.5–4, %13.319.2
 - Level 4.5+ (most overweight), %8.03.7
BMI at age 18 years, kg/m221.1 (3.1)20.9 (2.2)
BMI at biopsy, kg/m223.1 (5.8)21.9 (5.8)
Age at menarche, years12.6 (1.4)12.3 (1.3)
Parous at biopsy, %94.092.9
 Parity at biopsy (among parous women)3.1 (1.5)3.2 (1.6)
 Age at first birth, years (among parous women)24.6 (3.4)25.2 (3.0)
Premenopausal, %74.974.2
Age at menopause (among postmenopausal women at biopsy)45.5 (7.2)47.2 (4.4)
Ever oral contraceptive use51.061.2
Ever smoking50.466.3
Family history of breast cancer, %17.029.8
Adolescent alcohol drinker, %52.356.4
Cumulative average lifetime alcohol consumptionb, g/d4.7 (7.1)3.8 (3.6)
Cumulative average adult physical activityc, MET-hr/wk15.9 (19.1)11.2 (9.9)

NOTE: Values are median (IQR), means (SD), or percentages and are standardized to the age distribution of the study population. Values of polytomous variables may not sum to 100% due to rounding. IQR is the difference between the 75th and the 25th percentiles.

Abbreviation: BMI, body mass index.

  • aAmong 69 breast cancer cases, 54 cases were invasive cancers and 15 cases were in situ cancers. Among these 69 cases, 18 cases were ipsilateral, 25 cases were contralateral, and 8 cases were bilateral with respect to the index benign biopsies (the remaining 18 cases were from the unknown side of the breast).

  • bValue is not age adjusted.