Table 5.
Relative risks and 95% confidence intervals (CI) of invasive breast cancer according to quintiles of caffeine consumption, by tumor characteristics
| Characteristics | Quintile of Total Caffeine
|
|||||
|---|---|---|---|---|---|---|
| 1 (lowest) | 2 | 3 | 4 | 5 (highest) | P value for trend* | |
| Hormone receptor status | ||||||
| ER+PR+ | ||||||
| No. of cases | 178 | 147 | 164 | 168 | 146 | |
| Person-years | 75841 | 76017 | 76145 | 76122 | 76409 | |
| Incidence rate (cases per 100000 person-years) | 234.7 | 193.4 | 215.4 | 220.7 | 191.1 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.85 (0.68–1.05) | 0.93 (0.76–1.16) | 0.95 (0.77–1.18) | 0.84 (0.67–1.05) | .31 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.85 (0.68–1.06) | 0.93 (0.75–1.16) | 0.93 (0.75–1.16) | 0.84 (0.67–1.06) | .30 |
| ER+PR− | ||||||
| No. of cases | 24 | 20 | 27 | 27 | 27 | |
| Person-years | 76569 | 76664 | 76780 | 76769 | 77017 | |
| Incidence rate (cases per 100000 person-years) | 31.3 | 26.1 | 35.2 | 35.2 | 35.1 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.85 (0.47–1.54) | 1.15 (0.67–2.00) | 1.13 (0.65–1.95) | 1.17 (0.67–2.03) | .36 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.84 (0.46–1.53) | 1.10 (0.62–1.94) | 1.28 (0.72–2.26) | 1.38 (0.78–2.46) | .11 |
| ER−PR− | ||||||
| No. of cases | 25 | 26 | 41 | 32 | 42 | |
| Person-years | 76584 | 76650 | 76668 | 76751 | 76911 | |
| Incidence rate (cases per 100000 person-years) | 32.6 | 33.9 | 53.5 | 41.7 | 54.6 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 1.03 (0.60–1.79) | 1.64 (1.00–2.70) | 1.28 (0.76–2.15) | 1.67 (1.01–2.73) | .03 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.98 (0.56–1.69) | 1.60 (0.96–2.65) | 1.27 (0.74–2.17) | 1.68 (1.01–2.81) | .02 |
| Tumor size | ||||||
| ≤2 cm | ||||||
| No. of cases | 195 | 140 | 184 | 177 | 167 | |
| Person-years | 75696 | 75900 | 75934 | 76008 | 76226 | |
| Incidence rate (cases per 100000 person-years) | 257.6 | 184.5 | 242.3 | 232.9 | 219.1 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.73 (0.59–0.91) | 0.96 (0.78–1.17) | 0.91 (0.75–1.12) | 0.87 (0.71–1.07) | .78 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.73 (0.59–0.91) | 0.95 (0.77–1.17) | 0.90 (0.73–1.10) | 0.86 (0.69–1.06) | .61 |
| >2 cm | ||||||
| No. of cases | 38 | 59 | 58 | 60 | 59 | |
| Person-years | 76418 | 76355 | 76531 | 76522 | 76705 | |
| Incidence rate (cases per 100000 person-years) | 49.7 | 77.3 | 75.8 | 78.4 | 76.9 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 1.60 (1.06–2.40) | 1.56 (1.04–2.35) | 1.60 (1.06–2.40) | 1.60 (1.07–2.41) | .08 |
| Multivariate adjusted‡ | 1.00 [Reference] | 1.56 (1.03–2.35) | 1.53 (1.01–2.32) | 1.69 (1.12–2.55) | 1.79 (1.18–2.72) | .02 |
| Lymph node metastasis | ||||||
| Absent | ||||||
| No. of cases | 177 | 132 | 171 | 185 | 174 | |
| Person-years | 75732 | 75953 | 75883 | 75932 | 76119 | |
| Incidence rate (cases per 100000 person-years) | 233.7 | 173.8 | 225.3 | 243.6 | 228.6 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.76 (0.61–0.95) | 0.98 (0.80–1.21) | 1.06 (0.86–1.30) | 1.01 (0.82–1.24) | .20 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.76 (0.61–0.96) | 0.98 (0.79–1.22) | 1.04 (0.84–1.29) | 1.01 (0.81–1.25) | .23 |
| Present | ||||||
| No. of cases | 53 | 67 | 65 | 48 | 51 | |
| Person-years | 76317 | 76298 | 76472 | 76539 | 76772 | |
| Incidence rate (cases per 100000 person-years) | 69.4 | 87.8 | 85.0 | 62.7 | 66.4 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 1.28 (0.89–1.84) | 1.23 (0.85–1.76) | 0.90 (0.61–1.33) | 0.96 (0.65–1.41) | .29 |
| Multivariate adjusted‡ | 1.00 [Reference] | 1.23 (0.86–1.77) | 1.15 (0.80–1.67) | 0.92 (0.62–1.36) | 0.98 (0.66–1.45) | .43 |
| Histological grading and differentiation | ||||||
| Well | ||||||
| No. of cases | 56 | 49 | 54 | 44 | 61 | |
| Person-years | 76170 | 76213 | 76281 | 76383 | 76524 | |
| Incidence rate (cases per 100000 person-years) | 73.5 | 64.3 | 70.8 | 57.6 | 79.7 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.90 (0.61–1.31) | 0.99(0.68–1.43) | 0.79 (0.53–1.17) | 1.12 (0.78–1.62) | .55 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.91 (0.62–1.34) | 1.02 (0.70–1.50) | 0.78 (0.52–1.17) | 1.21 (0.83–1.76) | .40 |
| Moderately | ||||||
| No. of cases | 115 | 76 | 102 | 103 | 92 | |
| Person-years | 75909 | 76077 | 76062 | 76074 | 76354 | |
| Incidence rate (cases per 100000 person-years) | 151.5 | 99.9 | 134.1 | 135.4 | 120.5 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 0.68 (0.51–0.91) | 0.90 (0.69–1.18) | 0.91 (0.70–1.19) | 0.82 (0.63–1.08) | .68 |
| Multivariate adjusted‡ | 1.00 [Reference] | 0.68 (0.51–0.91) | 0.89 (0.68–1.17) | 0.92 (0.70–1.21) | 0.82 (0.62–1.10) | .70 |
| Poorly | ||||||
| No. of cases | 46 | 56 | 57 | 65 | 53 | |
| Person-years | 76216 | 76187 | 76223 | 76260 | 76556 | |
| Incidence rate (cases per 100000 person-years) | 60.4 | 73.5 | 74.8 | 85.2 | 69.2 | |
| Relative risk (95% CI) | ||||||
| Age and treatment adjusted† | 1.00 [Reference] | 1.23 (0.83–1.81) | 1.25 (0.85–1.84) | 1.40 (0.96–2.04) | 1.15 (0.77–1.70) | .52 |
| Multivariate adjusted‡ | 1.00 [Reference] | 1.17 (0.79–1.73) | 1.15 (0.77–1.71) | 1.39 (0.94–2.04) | 1.11 (0.74–1.67) | .56 |
*
The test for trend was calculated using median intake of caffeine consumption in each category as a continuous variable.
†
Adjustments for age and randomized treatment assignment
‡
Adjustments for variables in multivariable analysis in footnote to Table 2