White blood cell DNA methylation and risk of breast cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO)

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 OR^a	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 OR^a	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 OR^a,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 OR^a,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 OR^a,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 OR^a,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 OR^a,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

ISSN: 1465-542X