Table 2.

Summary of study population characteristics by biopsy category^*

	Biopsy category
Characteristic	Benign, no atypia	Infiltrating cancer or DCIS	Premalignant	No biopsy (benign)	P
Mean age at menarche, y†	13	12	13	13	.9997
Mean age at first pregnancy, y†	25	22	24	24	.8622
% Nulliparous	79.1	100.0	66.7	75.8	.9299
Mean age at diagnosis, y†	36	38	38	35	.0959
Menopausal status					.0307
Premenopausal	86	6	6	433
Postmenopausal	6	0	0	48
Perimenopausal	0	0	1	4
Screening breast EIS result					<.001
Negative	87	4	4	473
Positive	5	2	3	13
Clinical breast examination result					<.001
No findings	19	2	4	359
Not suspicious	55	1	2	124
Suspicious	18	3	1	3
Hormone replacement therapy					.9460
Current	1	0	0	14
Past	1	0	0	3
Never	90	6	7	469
Bra cup size					.0094
A	4	3	0	39
B	25	1	3	123
C	18	0	1	110
D+	6	1	1	65
Not recorded	39	1	2	149
Mammogram results					<.001
BIRADS 0	3	0	3	8
BIRADS I or II	27	0	2	163
BIRADS III	6	0	0	30
BIRADS IV	26	3	2	4
BIRADS V	0	3	0	1
No mammogram	30	0	0	280
Family history category					.1035
One first degree	7	1	0	51
One second degree	18	1	2	87
One first degree and one or more second degree	0	1	0	6
Two or more first degree	6	0	2	42
Two or more second degree	55	2	3	266
No significant family history	6	1	0	34
Gail model 5-year risk category, %					<.001
<1.66	86	2	5	441
≥1.66	4	3	1	22
Not recorded	2	1	1	23

*BIRADS indicates Breast Imaging Reporting and Data System; EIS, electrical impedance scanning; and DCIS, ductal carcinoma in situ.

†P value of cancer and premalignant populations compared with benign population.