Measurements of Breast Density: No Ratio for a Ratio

DOI: 10.1158/1055-9965.EPI-05-0824 Published November 2005

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Figure 1.
Manually traced contours of total breast size (outer contour) and dense tissue (inner contour) on a digitized xero-film mammogram.

Table 1.

Distribution of density and/or breast cancer risk factors in study population

	Mean (SD)	Range
Age at examination, y	56.4 (4.16)	49.2-65.8
Weight, kg	67.7 (9.83)	43.5-105.0
Height, m	1.63 (0.06)	1.46-1.87
BMI, kg/m²	25.6 (3.41)	17.8-42.8
Age at menarche,* y	13.5 (1.57)	11.0-18.3
Age at menopause,^† y	49.6 (3.78)	32.0-60.0
Time since menopause,^† y	7.5 (5.36)	0.1-28.5
Parity (no. children)	2.4 (1.91)	0-9
Age at first childbirth,^‡ y	27.3 (4.11)	18.1-39.9

	n (proportion)
Parous (yes)	332 (79%)
Current oral contraceptive use (yes)	8 (2%)
Ever used oral contraceptives (yes)	43 (10%)
Used hormone therapy in the last 12 mo (yes)	47 (11%)
Ever smoked (yes)	116 (28%)
Family history of breast cancer (yes)^§	26 (6%)

	Median (interquartile range)	Range
Breast size, cm²	123.7 (94.7-162.6)	29.1-345.3
Absolute amount dense tissue, cm²	26.4 (15.2-46.4)	0.3-138.0
Absolute amount nondense tissue, cm²	87.8	55.6-130.6
Percent dense	23.2	11.6-43.6

Table 2.

Geometric means of absolute density, absolute nondensity and relative density and trend tests over groups of characteristics

	n	Absolute dense, cm²	Absolute nondense, cm²	Percent dense, %
Age at examination, y
<54	139	31.3	72.0	26.1
54-58	140	22.2	80.1	18.9
>58	139	18.2	92.3	14.3
P for trend	418	<0.01	<0.01	<0.01
Weight, kg
<63	140	26.2	53.0	29.0
63-70	143	22.6	91.3	17.6
>70	135	21.2	114.6	13.8
P for trend	418	0.06	<0.01	<0.01
Height, m
<1.60	133	21.3	84.7	17.5
1.60-1.65	151	23.6	81.0	19.4
>1.65	134	25.2	80.2	20.8
P for trend	418	0.15	0.51	0.18
BMI, kg/m²
<20	12	28.3	21.7	52.0
20 to <25	187	26.6	62.0	26.4
25 to <30	171	21.6	101.1	15.8
<30	41	17.3	156.1	8.9
P for trend	418	0.07	<0.01	<0.01
Age at menarche, y
<13	122	21.4	96.6	16.1
13-14	178	23.4	72.3	21.1
>14	116	25.5	82.8	20.5
P for trend	416	0.16	0.07	0.08
Age at menopause, y
<49	107	19.5	83.1	16.8
49-51	139	19.9	90.9	15.8
>51	115	27.0	77.7	22.5
P for trend	361	0.01	0.42	0.04
Time since menopause, y
<4	120	28.3	74.4	23.7
4-9	121	21.1	81.5	18.1
>9	120	17.4	98.5	13.5
P for trend	361	<0.01	<0.01	<0.01
Parous
Yes	332	22.2	87.8	17.7
No	86	28.1	62.5	26.3
P	418	0.04	<0.01	<0.01
Age at first childbirth, y
<25	110	20.8	92.6	16.2
25-28	111	22.6	81.7	19.1
>28	111	23.1	89.6	17.9
P for trend	332	0.42	0.70	0.50
Parity (no. children)
0	86	28.1	62.5	26.3
1	53	26.9	82.3	21.3
2	93	28.5	77.3	23.6
3	89	20.2	92.4	15.8
>3	97	17.2	98.2	13.5
P for trend	418	<0.01	<0.01	<0.01
Current oral contraceptive use
Yes	8	31.3	66.2	28.8
No	410	23.2	82.2	19.1
P	418	0.87	0.36	0.29
Ever used oral contraceptives
Yes	43	28.0	78.3	23.5
No	375	22.8	82.3	18.8
P	418	0.18	0.64	0.19
Used hormone therapy in the last 12 mo
Yes	47	27.8	75.9	23.9
No	371	22.8	82.7	18.7
P	418	0.18	0.41	0.14
Ever smoked
Yes	116	27.4	67.5	25.1
No	302	21.9	88.3	17.3
P	418	0.03	<0.01	<0.01
Family history of breast cancer*
Yes	26	23.6	77.4	20.7
No	382	23.2	82.7	19.0
P	408	0.92	0.62	0.71

NOTE: Geometric means were calculated in tertiles of continuous variables or binary groups of dichotomous variables. For BMI, standard classes were used and for parity, nominal classes were used, with a truncation at >3. Tests for linear trends were done through ANOVA with an F test on the geometric data.
↵* Defined as one or more affected mother and/or sister.

Table 3.

Multivariate determinants of absolute density, absolute nondensity and relative density

↵* Back-transformed β's from analyses based on square root–transformed measurements of density.

Table 4.

Cross-tabulation of quartiles of absolute amount of density by quartiles of relative amount of density

↵* Range of the absolute amount of dense tissue (in cm²) corresponding to the quartile of relative density.
↵† Range of the absolute amount of density (in cm²) within each quartile.
↵‡ Range of the relative amount of density (in %) corresponding to the quartile of absolute amount of density.