Table 4. Odds ratios (95% confidence interval) of developing subsequent breast cancer according to cross-classified groups of Ki67 and p27, Ki67 and ER, p27 and ER in normal breast tissue among premenopausal women in the Nurses’ Health Study and the Nurses’ Health Study II.

The fraction of p27⁺, ER⁺, and Ki67⁺ in normal breast tissue were dichotomized around the median (above vs. below median percentage of stain-positive cells). Odds ratio and 95% confidence intervals were estimated using matching factors only model: age at diagnosis (continuous, years), calendar year of biopsy (<1970, 1970–1980, 1980+), time since biopsy (continuous, years).

Tissue expression		Case	Control	OR (95% CI)
Ki67 and p27 (cross-classified)
Low Ki67 (<1.15 %)	Low p27 (<16.6 %)	4	39	1.0 (Ref)
	High p27 (16.6+ %)	6	35	1.99 (0.49, 8.0)
High Ki67 (1.15+ %)	Low p27 (<16.6 %)	14	30	5.08 (1.43, 18.1)
	High p27 (16.6+ %)	11	31	3.5 (0.98, 12.5)
Ki67 and ER (cross-classified)
Low Ki67 (<1.15 %)	Low ER (<5.3 %)	6	43	1.0 (Ref)
	High ER (5.3+ %)	3	26	1.08 (0.23, 5.01)
High Ki67 (1.15+ %)	Low ER (<5.3 %)	20	33	4.68 (1.63, 13.5)
	High ER (5.3+ %)	3	25	0.90 (0.20, 4.08)
p27 and ER (cross-classified)
Low ER (<5.3 %)	Low p27 (<16.6 %)	18	61	1.0 (Ref)
	High p27 (16.6+ %)	18	43	1.51 (0.69, 3.31)
High ER (5.3+ %)	Low p27 (<16.6 %)	6	18	1.27 (0.43, 3.79)
	High p27 (16.6+ %)	4	40	0.39 (0.12, 1.25)