Table 1 Distribution of CBC case and unilateral breast cancer controls
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 |