Table 4.
Quartile level of WBC DNA methylation and risk of breast cancer by date of DNA extraction, and by time between blood collection and diagnosis, stratified by DNA extraction method
| Quartiles of DNA methylation | ||||
|---|---|---|---|---|
| Q4 (high) | Q3 | Q2 | Q1 (low) | |
| Period of DNA extraction | ||||
| Previously extracted DNA | ||||
| Adjusted ORa | 1. 0 (referent) | 0.99 | 1.01 | 1.44 |
| 95% CI | (0.5–1.9) | (0.5–2.0) | (0.8–2.7) | |
| Cases, controls | 33, 36 | 33, 36 | 34, 36 | 51, 39 |
| Newly extracted DNA | ||||
| Adjusted ORa | 1.0 (referent) | 0.84 | 0.82 | 0.61 |
| 95% CI | (0.5–1.3) | (0.5–1.3) | (0.4–1.0) | |
| Cases, controls | 81, 65 | 74, 70 | 68, 66 | 54, 71 |
| Time from blood collection to diagnosis | ||||
| Previously extracted DNA | ||||
| 1 to <2 years | ||||
| Adjusted ORa,b | 1.0 (referent) | 0.99 | 1.16 | 1.41 |
| 95% CI | (0.4–2.7) | (0.4–3.0) | (0.6–3.6) | |
| Cases, controls | 11, 36 | 10, 36 | 13, 36 | 16, 39 |
| 2 to <4 years | ||||
| Adjusted ORa,b | 1.0 (referent) | 1.15 | 1.00 | 1.39 |
| 95% CI | (0.5–2.7) | (0.4–2.4) | (0.6–3.2) | |
| Cases, controls | 14, 36 | 16, 36 | 14, 36 | 21, 39 |
| ≥ 4 years | ||||
| Adjusted ORa,b | 1.0 (referent) | 0.89 | 0.97 | 1.53 |
| 95% CI | (0.3–2.8) | (0.3–3.1) | (0.6–4.3) | |
| Cases, controls | 8, 36 | 7, 36 | 7, 36 | 14, 39 |
| Newly extracted DNA | ||||
| 2 to <4 years | ||||
| Adjusted ORa,b | 1. 0 (referent) | 0.88 | 0.73 | 0.68 |
| 95% CI | (0.5–1.5) | (0.4–1.3) | (0.4–1.2) | |
| Cases, controls | 43, 65 | 43, 70 | 32, 66 | 33, 71 |
| ≥4 years | ||||
| Adjusted ORa,b | 1.0 (referent) | 0.80 | 1.00 | 0.51 |
| 95% CI | (0.4–1.5) | (0.6–1.8) | (0.3–1.0) | |
| Cases, controls | 38, 65 | 31, 70 | 36, 66 | 21, 71 |
aAdjusted for age and time at entry
bSame controls are used for each category of elapsed time from blood collection to diagnosis, within period of DNA extraction (previously extracted, newly extracted); OR Odds Ratio