. Author manuscript; available in PMC: 2016 Jan 28.

Published in final edited form as: Cancer Lett. 2014 Apr 28;356(2 0 0):231–243. doi: 10.1016/j.canlet.2014.04.018

Table 2.

Risk estimates for estrogen metabolite pathways or ratios and breast cancer risk in postmenopausal women in studies of over 300 cases only.

First author, year	Estrogen metabolite pathways or ratios^*	Cases/controls	Design/Biospecimen	Risk estimates^† (95% CI) for the top vs. bottom hormone category level	P_trend
Dallal, 2013^a [118]	2-OHE₁/16α-OHE₁ Ratio	385/723	Combined analysis/urine	1.02 (0.71–1.48)	0.9
Obi, 2011^b,^c [119]	2-OHE₁/16α-OHE₁ Ratio	1189/1888	Systematic review/urine& blood	0.75 (0.35–1.62) to 1.31 (0.53–3.18)	N/A
Dallal, 2014^d [121]	2-OHE₁/16α-OHE₁ Ratio		Case-cohort study within the B~FIT/blood	0.88 (0.59–1.32)	0.8
	2-pathway/16-pathway	407/496		0.6 (0.40–0.90)	0.002
	2-pathway/parent estrogens			0.69 (0.46–1.05)	0.01

Abbreviations: N/A, not available; 2-OHE₁, 2-hydroxyestrone; 16α-OHE₁, 16-alpha-hydroxyestrone; CI, confidence interval; PLCO, the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial; B~FIT, the Breast and Bone Follow-up to the Fracture Intervention Trial.

Parent estrogens include estrone and estradiol.

2-hydroxylation pathway: 2-hydroxyestrone, 2-methoxyestrone, 2-hydroxyestradiol, 2-methoxyestradiol, and 2-hydroxyestrone-3-methyl ether.

16-hydroxylation pathway: 16a-hydroxyestrone, estriol, 17-epiestriol, 16-ketoestradiol, and 16-epiestriol.

^†

Risk estimates for [118] and [119] refrences are odds ratios, but risk estimates for [121] reference are hazard ratios.

From individual studies cited in references [117], [137], and [143–145]. Reported odds ratio is based on tertile comparison.

Range of odds ratios with respective CIs. Reported odds ratios are based on tertile and quintile comparisons, respectively.

From individual studies cited in references [117], [137], and [144–148].

Reported hazard ratios are based on quintile comparisons.

Note: All studies adjusted or matched for different covariates affecting breast cancer risk. Also, results from Kabat [116], Fuhrman [120], and Falk [122] studies are not shown in this table. Number of cases in these studies includes 42, 277, and 215, respectively.