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Table 1 Characteristics of study participants

From: Mammographic density and risk of breast cancer by mode of detection and tumor size: a case-control study

  Screen-detected cases Interval cases  
  Cases (n = 244) Controls (n = 700) P Cases (n = 148) Controls (n = 446) P P a
Age at baseline, years 56 (8) 56 (8) 0.72 54 (8) 54 (8) 0.72 0.01
Age at mammogram, years 59 (7) 59 (7) 0.82 57 (7) 57 (7) 0.79 <0.01
Age at diagnosis, years 65 (7)    62 (7)    <0.001
Time between age at mammogram and reference age, years 6 (3) 6 (3) 0.58 5 (3) 5 (4) 0.93 0.12
Total energy intake, MJ/day 8.4 (2.9) 8.6 (3.5) 0.40 8.7 (3.2) 8.7 (3.1) 0.91 0.30
BMI, kg/m2
 All women 27.5 (4.9) 26.7 (4.9) 0.04 26.7 (5.3) 26.5 (4.8) 0.68 0.11
 Premenopausal 27.2 (5.7) 26.2 (5.0) 0.17 25.9 (4.9) 26.1 (4.6) 0.72 0.15
 Postmenopausal 27.6 (4.6) 27.0 (4.9) 0.10 27.2 (5.5) 26.7 (5.0) 0.41 0.51
BMI at age 18–21 years, kg/m2 21.5 (2.9) 21.5 (2.9) 0.86 21.4 (2.5) 21.5 (2.8) 0.54 0.66
Breast
 Total area, cm2 143.7 (60.9) 137.8 (57.6) 0.17 125.0 (56.9) 133.4 (60.3) 0.14 <0.01
 Non-dense area, cm2 124.2 (62.1) 120.9 (58.8) 0.47 96.5 (55.6) 115.3 (60.6) <0.001 <0.0001
 Dense area, cm2 19.6 (21.7) 16.8 (20.6) 0.08 28.5 (24.5) 18.1 (19.4) <0.0001 <0.001
 Percent dense area 15.5 (15.7) 14.0 (15.3) 0.18 25.2 (17.9) 15.4 (14.7) <0.0001 <0.0001
Country of birth, n (%)        
 Anglo Saxon/other 204 (84) 583 (83) 0.99 123 (83) 371 (83) 0.99 0.70
 Italy 25 (10) 74 (11)   13 (9) 40 (9)   
 Greece 15 (6) 43 (6)   12 (8) 35 (8)   
Age at menarche, years n (%)
 <12 47 (19) 125 (18) 0.92 31 (21) 75 (17) 0.69 0.74
 12 52 (21) 145 (21)   25 (17) 86 (19)   
 13 55 (23) 169 (24)   36 (24) 111 (25)   
 14+ 88 (36) 261 (37)   56 (38) 174 (39)   
Parity and lactation, n (%),
 Nulliparous 38 (16) 84 (12) 0.03 25 (17) 62 (14) 0.63 0.22
 Parous, never lactated 10 (4) 61 (9)   12 (8) 34 (8)   
 Parous, lactated 190 (78) 542 (77)   108 (73) 343 (77)   
Menopausal status n (%)
 Premenopausal 69 (28) 195 (28) 0.88 59 (40) 170 (38) 0.72 0.02
 Postmenopausal 174 (71) 504 (72)   89 (60) 275 (62)   
Hormone replacement therapy use, n (%)
 Never 169 (69) 493 (70) 0.75 98 (66) 323 (72) 0.17 0.55
 Ever 74 (30) 205 (29)   49 (33) 122 (27)   
Oral contraceptive use, n (%)
 Never 93 (38) 283 (40) 0.53 58 (39) 157 (35) 0.4 0.86
 Ever 150 (61) 415 (59)   90 (61) 287 (64)   
Alcohol consumption, n (%)
 Lifetime abstainers 109 (45) 257 (37) 0.10 43 (29) 160 (36) 0.3 <0.01
 Ex-drinkers 13 (5) 24 (3)   3 (2) 13 (3)   
 Low intake, 1–19 g/day 97 (40) 337 (48)   78 (53) 223 (50)   
 Medium intake, 20–39 g/day 19 (8) 61 (9)   20 (14) 38 (9)   
 High intake, ≥40 g/day 6 (2) 21 (3)   4 (3) 12 (3)   
Family history of breast cancerb, n (%)
 No 185 (76) 548 (78) 0.08 101 (68) 341 (76) <0.001 0.18
 Yes 38 (16) 77 (11)   30 (20) 43 (10)   
ER, n (%)
 Positive 188 (77.0)    94 (63.5)    <0.01
 Negative 45 (18.4)    45 (30.4)    
PR, n (%)
 Positive 126 (51.6)    57 (38.5)    0.02
 Negative 106 (43.4)    80 (54.1)    
HER2, n (%)
 Positive 73 (29.9)    41 (27.7)    0.64
 Negative 153 (62.7)    96 (64.9)    
Grade n (%)
 Well-differentiated 62 (25.4)    24 (16.2)    <0.01
 Moderately differentiated 104 (42.6)    52 (35.1)    
 Poorly differentiated 65 (26.6)    61 (41.2)    
Nodal status, n (%)
 Positive 39 (16.0)    65 (43.9)    <0.001
 Negative 190 (77.9)    71 (48.0)    
Tumor size, n (%)
 <1 cm 76 (31.1)    25 (16.9)    <0.001
 1–2 cm 116 (47.5)    51 (34.5)    
 ≥2 cm 49 (20.1)    65 (43.9)    
  1. Results are presented as mean (SD) unless stated otherwise. P values are for Pearson’s χ2 test or Fisher’s exact test for categorical variables and Student’s two-sided t test for continuous variables. a P values are for tests comparing screen-detected cases with interval cases. bFamily history of breast cancer is defined as having any relative with breast cancer. BMI body mass index, SD standard deviation, ER estrogen receptor, PR progesterone receptor, HER2 human epidermal growth factor receptor-2