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Table 1 Distribution of CBC case and unilateral breast cancer controls

From: Change of mammographic density predicts the risk of contralateral breast cancer - a case-control study

   Cases Controls P-value*
Age at (first) diagnosis (%) ≤45 years 37 (18) 37 (18)  
  45 to 55 years 68 (32) 68 (32)  
  55 to 65 years 56 (27) 56 (27)  
  ≥65 years 50 (24) 50 (24) -
Calendar period of (first) diagnosis (%) 1976 to 1980 31 (15) 30 (14)  
  1981 to 1985 40 (19) 41 (19)  
  1986 to 1990 45 (21) 41 (19)  
  1991 to 1995 51 (24) 49 (23)  
  1996 to 2005 44 (21) 50 (24) -
Adjuvant therapy (%)* No adjuvant therapy 39 (18) 39 (18)  
  Radiotherapy only 57 (27) 57 (27)  
  Endocrine therapy 87 (41) 87 (41)  
  Chemotherapy 28 (13) 28 (13) -
Mean follow-up time in years   8.25 8.25 -
Percent density at (first) diagnosis (%) ≤5% 13 (6) 11 (5)  
  5 to 25% 87 (41) 87 (41)  
  25 to 50% 97 (46) 87 (41)  
  ≥50% 14 (7) 26 (12) 0.23
  Quartiles:    
Dense area at (first) diagnosis (%) ≤20 cm2 55 (26) 55 (26)  
  20 to 34 cm2 44 (21) 56 (27)  
  34 to 53 cm2 56 (27) 49 (23)  
  ≥53 cm2 56 (27) 51 (24) 0.79
Change in percent density until first Absolute decrease (>10%) 40 (19) 56 (27)  
follow-up mammogram (%) Stable density 164 (78) 143 (68)  
  Absolute increase (>10%) 7 (3) 12 (6) 0.07
Change in dense area until first Absolute decrease (>10 cm2) 61 (29) 75 (36)  
follow-up mammogram Stable density 131 (62) 113 (54)  
  Absolute increase (>10 cm2) 19 (9) 23 (11) 0.21
  Quartiles:    
Non-dense area at (first) diagnosis (%) ≤67 cm2) 42 (20) 60 (28)  
  67 to 93 cm2 58 (27) 43 (20)  
  93 to 127 cm2 50 (24) 55 (26)  
  ≥127 cm2 61 (29) 53 (25) 0.10
Mean time until first follow-up mammogram in years (SD)   1.56
(0.59)
1.54
(0.57)
0.56
Menopause status at diagnosis (%)** Premenopausal 89 (42) 84 (40)  
  Postmenopausal 119 (56) 124 (59) 0.62
  1. Subdivided by matching variables (age at diagnosis, calendar period of diagnosis, adjuvant therapy and follow-up time), exposure variables (dense area at diagnosis and change of dense area), potential confounding variables (non-dense area at diagnosis and time to first follow-up mammogram), and stratifying variable (menopause status).
  2. * P-value for Chi-square test of association when testing categorical variables and for Student's t-tests when testing the continuous variable (mean time until first follow-up mammogram).
  3. *Endocrine therapy may be with or without radiotherapy, chemotherapy may be with or without radiotherapy and/or endocrine therapy.
  4. ** Six patients had uncertain menopause status (for example, hysterectomy).