Background
Methods
Eligible cohort
Characteristics | Total | BMI < 21 | BMI 21-24 | BMI 25-29 | BMI 30-34 | BMI 35+ | Chi-square | % Obese | Trend | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
N | % | N | % | N | % | N | % | N | % | N | % | p-value | (BMI 30+) | p-value | |
Total | 1049 | 81 | 7.7 | 250 | 23.8 | 349 | 33.3 | 225 | 21.4 | 144 | 13.7 | 35.2 | |||
Adjuvant treatment | |||||||||||||||
Chemotherapy alone | 338 | 32.2 | 28 | 8.3 | 78 | 23.1 | 116 | 34.3 | 77 | 22.8 | 39 | 11.5 | 0.6 | 34.3 | |
Chemotherapy and hormonal therapy | 711 | 67.8 | 53 | 7.5 | 172 | 24.2 | 233 | 32.8 | 148 | 20.8 | 105 | 14.8 | 35.6 | ||
Age | |||||||||||||||
<40 | 132 | 12.6 | 16 | 12.1 | 34 | 25.8 | 34 | 25.8 | 30 | 22.7 | 18 | 13.6 | 0.4 | 36.4 | 0.7 |
40-59 | 678 | 64.6 | 52 | 7.7 | 162 | 23.9 | 230 | 33.9 | 137 | 20.2 | 97 | 14.3 | 34.5 | ||
60+ | 239 | 22.6 | 13 | 5.4 | 54 | 22.6 | 85 | 35.6 | 58 | 24.3 | 29 | 12.1 | 36.4 | ||
Menopausal status | |||||||||||||||
Pre-menopause | 474 | 45.2 | 44 | 9.3 | 129 | 27.2 | 150 | 31.6 | 93 | 19.6 | 58 | 12.2 | 0.06 | 31.9 | 0.13 |
Peri-menopause | 65 | 6.2 | 0 | 0.0 | 16 | 24.6 | 22 | 33.8 | 18 | 27.7 | 9 | 13.8 | 41.5 | ||
Post-menopause | 506 | 48.2 | 37 | 7.3 | 105 | 20.8 | 176 | 34.8 | 113 | 22.3 | 75 | 14.8 | 37.2 | ||
Missing/unknown | 4 | 0.4 | 0 | 0.0 | 0 | 0.0 | 1 | 25 | 1 | 25.0 | 2 | 50.0 | 75.0 | ||
Year of diagnosis | |||||||||||||||
2000-2002 | 190 | 18.1 | 16 | 8.4 | 51 | 26.8 | 66 | 34.7 | 40 | 21.1 | 17 | 8.9 | 0.5 | 30.0 | 0.2 |
2003-2005 | 213 | 20.3 | 17 | 8.0 | 52 | 24.4 | 64 | 30 | 47 | 22.1 | 33 | 15.5 | 37.6 | ||
2006-2008 | 230 | 21.9 | 16 | 7.0 | 61 | 26.5 | 72 | 31.3 | 55 | 23.9 | 26 | 11.3 | 35.2 | ||
2009-2011 | 218 | 20.8 | 17 | 7.8 | 40 | 18.3 | 77 | 35.3 | 48 | 22.0 | 36 | 16.5 | 38.5 | ||
2012-2014 | 198 | 18.9 | 15 | 7.6 | 46 | 23.2 | 70 | 35.4 | 35 | 17.7 | 32 | 16.2 | 33.8 | ||
Ethnicity | |||||||||||||||
European | 793 | 75.6 | 69 | 8.7 | 204 | 25.7 | 283 | 35.7 | 158 | 19.9 | 79 | 10.0 | <0.0001 | 29.9 | |
Maori | 194 | 18.5 | 7 | 3.6 | 34 | 17.5 | 47 | 24.2 | 55 | 28.4 | 51 | 26.3 | 54.6 | ||
Pacific | 32 | 3.1 | 0 | 0.0 | 4 | 12.5 | 6 | 18.8 | 8 | 25.0 | 14 | 43.8 | 68.8 | ||
Others | 30 | 2.9 | 5 | 16.7 | 8 | 26.7 | 13 | 43.3 | 4 | 13.3 | 0 | 0.0 | 13.3 | ||
Deprivation score (higher means greater deprivation) | |||||||||||||||
1-2 | 127 | 12.1 | 7 | 5.5 | 40 | 31.5 | 47 | 37 | 21 | 16.5 | 12 | 9.4 | 0.2 | 26.0 | 0.002 |
3-4 | 119 | 11.3 | 14 | 11.8 | 31 | 26.1 | 37 | 31.1 | 18 | 15.1 | 19 | 16.0 | 31.1 | ||
5-6 | 245 | 23.4 | 18 | 7.3 | 62 | 25.3 | 84 | 34.3 | 52 | 21.2 | 29 | 11.8 | 33.1 | ||
7-8 | 285 | 27.2 | 20 | 7.0 | 67 | 23.5 | 91 | 31.9 | 62 | 21.8 | 45 | 15.8 | 37.5 | ||
9-10 | 272 | 25.9 | 22 | 8.1 | 49 | 18.0 | 90 | 33.1 | 72 | 26.5 | 39 | 14.3 | 40.8 | ||
Missing/unknown | 1 | 0.1 | 0 | 0.0 | 1 | 100.0 | 0 | 0 | 0 | 0.0 | 0 | 0.0 | 0.0 | ||
Area of residence | |||||||||||||||
Urban | 614 | 58.5 | 52 | 8.5 | 143 | 23.3 | 197 | 32.1 | 131 | 21.3 | 91 | 14.8 | 0.2 | 36.2 | |
Semi-urban or rural | 406 | 38.7 | 29 | 7.1 | 94 | 23.2 | 144 | 35.5 | 89 | 21.9 | 50 | 12.3 | 34.2 | ||
Missing/unknown | 29 | 2.8 | 0 | 0.0 | 13 | 44.8 | 8 | 27.6 | 5 | 17.2 | 3 | 10.3 | 27.6 | ||
Comorbidity (C3 index score) | |||||||||||||||
0 | 912 | 86.9 | 75 | 8.2 | 226 | 24.8 | 312 | 34.2 | 187 | 20.5 | 112 | 12.3 | 0.05 | 32.8 | <0.001 |
1 | 75 | 7.1 | 4 | 5.3 | 13 | 17.3 | 20 | 26.7 | 21 | 28.0 | 17 | 22.7 | 50.7 | ||
2 | 40 | 3.8 | 1 | 2.5 | 7 | 17.5 | 11 | 27.5 | 11 | 27.5 | 10 | 25.0 | 52.5 | ||
3+ | 22 | 2.1 | 1 | 4.5 | 4 | 18.2 | 6 | 27.3 | 6 | 27.3 | 5 | 22.7 | 50.0 | ||
Screen-detected | |||||||||||||||
Yes | 303 | 28.9 | 17 | 5.6 | 57 | 18.8 | 117 | 38.6 | 72 | 23.8 | 40 | 13.2 | 0.02 | 37.0 | |
No | 746 | 71.1 | 64 | 8.6 | 193 | 25.9 | 232 | 31.1 | 153 | 20.5 | 104 | 13.9 | 34.5 | ||
Stage at diagnosis | |||||||||||||||
I | 147 | 14 | 15 | 10.2 | 38 | 25.9 | 47 | 32 | 28 | 19.0 | 19 | 12.9 | 0.5 | 32.0 | 0.06 |
II | 537 | 51.2 | 34 | 6.3 | 137 | 25.5 | 186 | 34.6 | 114 | 21.2 | 66 | 12.3 | 33.5 | ||
III | 309 | 29.5 | 25 | 8.1 | 67 | 21.7 | 97 | 31.4 | 70 | 22.7 | 50 | 16.2 | 38.8 | ||
IV | 56 | 5.3 | 7 | 12.5 | 8 | 14.3 | 19 | 33.9 | 13 | 23.2 | 9 | 16.1 | 39.3 | ||
Grade | |||||||||||||||
I | 83 | 7.9 | 7 | 8.4 | 27 | 32.5 | 27 | 32.5 | 14 | 16.9 | 8 | 9.6 | 0.6 | 26.5 | 0.7 |
II | 512 | 48.8 | 35 | 6.8 | 120 | 23.4 | 167 | 32.6 | 113 | 22.1 | 77 | 15.0 | 37.1 | ||
III | 425 | 40.5 | 36 | 8.5 | 100 | 23.5 | 145 | 34.1 | 89 | 20.9 | 55 | 12.9 | 33.9 | ||
Missing/unknown | 29 | 2.8 | 3 | 10.3 | 3 | 10.3 | 10 | 34.5 | 9 | 31.0 | 4 | 13.8 | 44.8 | ||
Histology | |||||||||||||||
Ductal | 898 | 85.6 | 71 | 7.9 | 214 | 23.8 | 295 | 32.9 | 188 | 20.9 | 130 | 14.5 | 0.5 | 35.4 | |
Lobular | 94 | 9 | 8 | 8.5 | 21 | 22.3 | 30 | 31.9 | 25 | 26.6 | 10 | 10.6 | 37.2 | ||
Other | 57 | 5.4 | 2 | 3.5 | 15 | 26.3 | 24 | 42.1 | 12 | 21.1 | 4 | 7.0 | 28.1 | ||
ER/PR | |||||||||||||||
ER+/PR+ | 515 | 49.1 | 37 | 7.2 | 124 | 24.1 | 166 | 32.2 | 115 | 22.3 | 73 | 14.2 | 0.9 | 36.5 | |
ER+/PR- | 216 | 20.6 | 20 | 9.3 | 49 | 22.7 | 75 | 34.7 | 38 | 17.6 | 34 | 15.7 | 33.3 | ||
ER-/PR+ | 22 | 2.1 | 2 | 9.1 | 5 | 22.7 | 6 | 27.3 | 5 | 22.7 | 4 | 18.2 | 40.9 | ||
ER-/PR- | 270 | 25.7 | 20 | 7.4 | 64 | 23.7 | 92 | 34.1 | 62 | 23.0 | 32 | 11.9 | 34.8 | ||
Missing/unknown | 26 | 2.5 | 2 | 7.7 | 8 | 30.8 | 10 | 38.5 | 5 | 19.2 | 1 | 3.8 | 23.1 | ||
HER-2 | |||||||||||||||
Positive | 274 | 26.1 | 20 | 7.3 | 60 | 21.9 | 90 | 32.8 | 57 | 20.8 | 47 | 17.2 | 0.7 | 38.0 | |
Equivocal | 27 | 2.6 | 1 | 3.7 | 7 | 25.9 | 7 | 25.9 | 8 | 29.6 | 4 | 14.8 | 44.4 | ||
Negative | 554 | 52.8 | 47 | 8.5 | 128 | 23.1 | 189 | 34.1 | 119 | 21.5 | 71 | 12.8 | 34.3 | ||
Missing/unknown | 194 | 18.5 | 13 | 6.7 | 55 | 28.4 | 63 | 32.5 | 41 | 21.1 | 22 | 11.3 | 32.5 | ||
Primary treatment (RT = radiotherapy) | |||||||||||||||
Breast conserving surgery with RT | 451 | 43 | 29 | 6.4 | 99 | 22.0 | 152 | 33.7 | 111 | 24.6 | 60 | 13.3 | 0.1 | 37.9 | |
Breast conserving surgery, no RT | 45 | 4.3 | 3 | 6.7 | 17 | 37.8 | 15 | 33.3 | 6 | 13.3 | 4 | 8.9 | 22.2 | ||
Mastectomy with RT | 379 | 36.1 | 33 | 8.7 | 93 | 24.5 | 124 | 32.7 | 69 | 18.2 | 60 | 15.8 | 34.0 | ||
Mastectomy, no RT | 130 | 12.4 | 11 | 8.5 | 35 | 26.9 | 47 | 36.2 | 24 | 18.5 | 13 | 10.0 | 28.5 | ||
No primary surgery | 44 | 4.2 | 5 | 11.4 | 6 | 13.6 | 11 | 25 | 15 | 34.1 | 7 | 15.9 | 50.0 | ||
Total breast conserving surgery | 496 | 47.3 | 32 | 13.1 | 116 | 59.7 | 167 | 67.0 | 117 | 37.9 | 64 | 22.2 | 0.3 | 36.5 | |
Total mastectomy | 509 | 48.5 | 44 | 17.2 | 128 | 51.5 | 171 | 68.9 | 93 | 36.7 | 73 | 25.8 | 32.6 | ||
Total with RT | 830 | 79.1 | 62 | 15.1 | 192 | 46.5 | 276 | 66.4 | 180 | 42.8 | 120 | 29.1 | 0.02 | 36.1 | |
Total without RT | 175 | 16.7 | 14 | 15.1 | 52 | 64.7 | 62 | 69.5 | 30 | 31.8 | 17 | 18.9 | 26.9 | ||
Facility where primary treatment was undertaken | |||||||||||||||
Private | 377 | 35.9 | 34 | 9.0 | 112 | 29.7 | 141 | 37.4 | 54 | 14.3 | 36 | 9.5 | <0.0001 | 23.9 | |
Public | 672 | 64.1 | 47 | 7.0 | 138 | 20.5 | 208 | 31.0 | 171 | 25.4 | 108 | 16.1 | 41.5 |
Data
Statistical methods
Results
Patient features and associations with BMI (patients with chemotherapy)
Outcomes in relation to BMI (patients with chemotherapy)
Outcome | Follow-up period | BMI (kg/m2) | No of events | Crude HR (95% CI) | Adjusted HR (95% CI) |
---|---|---|---|---|---|
Breast cancer specific death | 0-10 yrs | <21 (N=81) | 43 | 1.70 (0.99, 2.91) | 1.13 (0.60, 2.14) |
21-24 (N=250) | 88 | 1.00 | 1.00 | ||
25-29 (N=349) | 107 | 0.99 (0.66, 1.47) | 0.96 (0.61, 1.51) | ||
30-34 (N=225) | 67 | 1.24 (0.82, 1.88) | 0.98 (0.62, 1.54) | ||
35+ (N=144) | 49 | 1.31 (0.81, 2.12) | 0.99 (0.57, 1.71) | ||
Whole study period | <21 | 44 | 1.66 (0.97, 2.84) | 1.11 (0.59, 2.09) | |
21-24 | 91 | 1.00 | 1.00 | ||
25-29 | 110 | 0.98 (0.66, 1.46) | 0.95 (0.61, 1.50) | ||
30-34 | 67 | 1.21 (0.80, 1.83) | 0.96 (0.62, 1.50) | ||
35+ | 49 | 1.28 (0.79, 2.07) | 0.96 (0.56, 1.67) | ||
Overall mortality | 0-10 yrs | <21 | 67 | 1.64 (0.98, 2.73) | 1.12 (0.61, 2.05) |
21-24 | 122 | 1.00 | 1.00 | ||
25-29 | 153 | 1.01 (0.69, 1.46) | 0.92 (0.60, 1.41) | ||
30-34 | 93 | 1.17 (0.79, 1.73) | 0.88 (0.57, 1.34) | ||
35+ | 65 | 1.37 (0.88, 2.16) | 1.05 (0.64, 1.73) | ||
Whole study period | <21 | 70 | 1.49 (0.89, 2.51) | 1.04 (0.57, 1.90) | |
21-24 | 130 | 1.00 | 1.00 | ||
25-29 | 163 | 0.97 (0.68, 1.40) | 0.87 (0.57, 1.32) | ||
30-34 | 100 | 1.18 (0.81, 1.72) | 0.89 (0.59, 1.33) | ||
35+ | 69 | 1.36 (0.87, 2.10) | 1.03 (0.63, 1.67) | ||
Death from other/unknown causes | 0-10 | <21 | 24 | 1.08 (0.22, 5.34) | 1.44 (0.21, 9.97) |
21-24 | 34 | 1.00 | 1.00 | ||
25-29 | 46 | 1.15 (0.41, 3.25) | 1.11 (0.33, 3.72) | ||
30-34 | 26 | 0.74 (0.21, 2.58) | 0.74 (0.21, 2.67) | ||
35+ | 16 | 1.64 (0.50, 5.43) | 1.55 (0.34, 7.18) | ||
Whole study period | <21 | 26 | 0.70 (0.14, 3.45) | 1.01 (0.19, 5.45) | |
21-24 | 39 | 1.00 | 1.00 | ||
25-29 | 53 | 0.98 (0.39, 2.43) | 0.78 (0.27, 2.29) | ||
30-34 | 33 | 1.04 (0.40, 2.72) | 1.15 (0.42, 3.11) | ||
35+ | 20 | 1.56 (0.54, 4.51) | 1.42 (0.40, 5.01) | ||
Loco-regional recurrence | 0-5 | <21 (N=81) | 13 | 1.04 (0.22, 4.98) | 1.24 (0.20, 7.64) |
21-24 (N=250) | 22 | 1.00 | 1.00 | ||
25-29 (N=349) | 23 | 0.87 (0.32, 2.40) | 1.13 (0.34, 3.73) | ||
30-34 (N=225) | 27 | 0.88 (0.28, 2.77) | 1.38 (0.36, 5.29) | ||
35+ (N=144) | 11 | 0.60 (0.12, 2.87) | 1.12 (0.16, 7.84) | ||
Whole study period | <21 | 17 | 1.58 (0.42, 6.02) | 2.08 (0.42, 10.23) | |
21-24 | 25 | 1.00 | 1.00 | ||
25-29 | 25 | 1.11 (0.42, 2.93) | 1.26 (0.41, 3.87) | ||
30-34 | 28 | 1.10 (0.37, 3.28) | 1.58 (0.44, 5.63) | ||
35+ | 12 | 0.63 (0.13, 3.04) | 1.17 (0.19, 7.21) | ||
Distant metastasis | 0-5 | <21 | 43 | 1.74 (0.66, 4.54) | 1.44 (0.51, 4.03) |
21-24 | 90 | 1.00 | 1.00 | ||
25-29 | 103 | 1.13 (0.57, 2.24) | 0.89 (0.44, 1.80) | ||
30-34 | 65 | 1.20 (0.56, 2.55) | 1.17 (0.51, 2.67) | ||
35+ | 62 | 1.62 (0.72, 3.64) | 1.69 (0.69, 4.11) | ||
Whole study period | <21 | 46 | 1.62 (0.67, 3.93) | 1.32 (0.52, 3.37) | |
21-24 | 103 | 1.00 | 1.00 | ||
25-29 | 127 | 1.38 (0.76, 2.53) | 1.05 (0.56, 1.94) | ||
30-34 | 87 | 1.50 (0.77, 2.90) | 1.23 (0.61, 2.49) | ||
35+ | 70 | 1.73 (0.82, 3.63) | 1.33 (0.61, 2.91) |
Subgroup analyses and quantitative analysis
BMI <24 | BMI 25-29.9 | BMI 30+ |
P value
| |||
---|---|---|---|---|---|---|
Total | No. | 331 | 349 | 369 | ||
Deaths 10 years, % | ||||||
All patients | 19.0 | 15.8 | 19.8 | P value | ||
Age | <40 | 132 | 20.0 | 38.0 | 20.0 | 0.1 |
40-59 | 678 | 18.2 | 10.9 | 19.7 | 0.02 | |
60+ | 239 | 29.2 | 35.4 | 35.4 | 0.9 | |
Menopause | Pre-menopause | 474 | 16.2 | 16.0 | 18.5 | 0.8 |
Peri-menopause | 65 | 6.3 | 13.6 | 11.1 | 0.8 | |
Post-menopause | 506 | 23.9 | 15.9 | 22.3 | 0.2 | |
Ethnicity* | Maori | 194 | 26.8 | 21.3 | 24.5 | 0.8 |
NZ European | 793 | 18.7 | 15.6 | 17.3 | 0.6 | |
Stage | 1, 2 | 684 | 8.9 | 9.9 | 8.4 | 0.9 |
3, 4 | 365 | 40.2 | 27.6 | 38.0 | 0.1 | |
Detection | Screen detected | 303 | 12.2 | 11.1 | 11.6 | 0.9 |
Symptomatic | 746 | 21.0 | 18.1 | 23.4 | 0.4 | |
Receptors | ER+, PR+ | 515 | 13.0 | 12.1 | 14.4 | 0.8 |
ER-, PR- | 270 | 15.8 | 13.6 | 22.2 | 0.3 | |
+/- | 238 | 30.1 | 25.0 | 27.7 | 0.7 | |
Systemic treatment | Chemo only | 338 | 33.0 | 24.1 | 32.8 | 0.2 |
Chemo + hormonal | 711 | 12.4 | 11.6 | 13.8 | 0.8 | |
Surgery | Breast conserving surgery | 496 | 14.2 | 11.4 | 9.9 | 0.5 |
Mastectomy | 509 | 20.4 | 16.4 | 24.1 | 0.2 | |
Radiotherapy | RT | 830 | 18.0 | 13.7 | 16.1 | 0.4 |
no RT | 175 | 22.4 | 23.6 | 37.5 | 0.09 | |
Health sector | Public | 672 | 22.2 | 16.4 | 20.4 | 0.3 |
Private | 377 | 15.1 | 14.9 | 17.8 | 0.8 |
Analysis of outcomes in all patients
Outcome | Follow-up period | BMI (kg/m2) | Unadjusted HR (95% CI) | Adjusted HR (95% CI) |
---|---|---|---|---|
Breast cancer specific death | 0-10 | <25 | 1.00 | 1.00 |
25-29 | 0.90 (0.70, 1.16) | 0.98 (0.74, 1.30) | ||
30+ | 0.97 (0.76, 1.25) | 1.10 (0.82, 1.46) | ||
Whole study period | <25 | 1.00 | 1.00 | |
25-29 | 0.90 (0.70, 1.15) | 0.97 (0.73, 1.29) | ||
30+ | 0.95 (0.74, 1.22) | 1.06 (0.80, 1.41) | ||
Overall mortality | 0-10 | <25 | 1.00 | 1.00 |
25-29 | 0.88 (0.71, 1.09) | 1.03 (0.82, 1.30) | ||
30+ | 0.91 (0.74, 1.12) | 0.96 (0.75, 1.22) | ||
Whole study period | <25 | 1.00 | 1.00 | |
25-29 | 0.88 (0.72, 1.08) | 1.01 (0.81, 1.26) | ||
30+ | 0.93 (0.76, 1.14) | 0.96 (0.76, 1.21) | ||
Death from other/unknown causes | 0-10 | <25 | 1.00 | 1.00 |
25-29 | 0.87 (0.59, 1.28) | 0.97 (0.66, 1.45) | ||
30+ | 0.79 (0.53, 1.17) | 0.84 (0.55, 1.29) | ||
Whole study period | <25 | 1.00 | 1.00 | |
25-29 | 0.89 (0.62, 1.27) | 0.98 (0.68, 1.41) | ||
30+ | 0.90 (0.63, 1.29) | 0.96 (0.65, 1.42) | ||
Loco-regional recurrence | 0-5 | <25 | 1.00 | 1.00 |
25-29 | 0.85 (0.42, 1.71) | 0.80 (0.39, 1.67) | ||
30+ | 1.57 (0.85, 2.87) | 1.82 (0.95, 3.48) | ||
Whole study period | <25 | 1.00 | 1.00 | |
25-29 | 0.76 (0.40, 1.44) | 0.74 (0.38, 1.44) | ||
30+ | 1.35 (0.77, 2.34) | 1.48 (0.81, 2.68) | ||
Distant metastasis | 0-5 | <25 | 1.00 | 1.00 |
25-29 | 0.95 (0.62, 1.46) | 0.94 (0.60, 1.47) | ||
30+ | 1.15 (0.76, 1.75) | 1.27 (0.81, 1.97) | ||
Whole study period | <25 | 1.00 | 1.00 | |
25-29 | 1.12 (0.77, 1.62) | 1.08 (0.74, 1.59) | ||
30+ | 1.33 (0.92, 1.91) | 1.35 (0.92, 1.98) |