The association of mammographic density with ductal carcinoma in situof the breast: the Multiethnic Cohort

Table 1 Characteristics of the study population by disease status

Covariate	Invasive breast cancer	Breast DCIS	Controls	P value^a
Sample size	482	119	667	-
Ethnicity (%)				0.19^b
Hawaiian	14.3	8.4	24.3
Japanese	46.5	55.5	43.8
Caucasian	32.6	28.6	28.0
Other	6.6	7.6	3.9
Age at diagnosis (years)	63.5	62.9	N/A	0.50^b
Age at recruitment (years)	60.0	59.6	56.7	0.58^b
Mean age at all mammograms (years)	59.8	59.1	59.7	0.70
Body mass index (kg/m²)	25.2	24.5	25.7	0.07
Time from first mammogram to diagnosis (years)	6.2	6.7	N/A	0.17^b
Family history of breast cancer (%)	16.8	16.8	12.0	0.05
Age at first birth (years)	25.0	25.1	24.7	0.65
Age at menarche (years)	13.1	12.9	13.1	0.47
Parous (%)	84.5	83.9	88.5	0.10
Number of children	2.4	2.2	2.6	0.02
Postmenopausal (%)	86.3	89.9	77.7	<0.0001
Ever HRT use (%)	67.2	73.9	69.3	0.01
Number of mammograms	3.2^c	3.4^c	2.4^c	<0.0001
Breast percent density^d	36.5	38.2	29.4	<0.0001
Breast dense area^d (cm²)	36.7	34.9	28.7	<0.0001
Total breast area^d (cm²)	114.5	106.9	118.9	0.08

Unless otherwise indicated, mean values are given. ^aP ascertained from t test or χ² test, as appropriate. ^bCompares only invasive breast cancer and breast DCIS cases. All other comparisons are of invasive breast cancer cases, breast DCIS cases, and controls. ^cThe range for number of mammograms is 11, 10, and 7 for invasive breast cancer, breast DCIS, and controls, respectively. ^dAdjusted for age at recruitment. DCIS, ductal carcinoma in situ; HRT, hormone replacement therapy.