BMC Cancer 2008, 8:130 http://www.biomedcentral.com/1471-2407/8/130 cer, and consumed more than one alcoholic beverage per week. A higher percentage of epithelial cells stained posi- tively for ER among cases than controls. Among controls, the ER level in nonneoplastic tissue was associated with age (Spearman correlation, rs = 0.49, p < 0.0001). After adjustment for age, fat intake was the only covariate asso- ciated with ER level (Spearman correlation, rs = 0.14, p = 0.01). Among controls, the PR level in nonneoplastic tis- sue was not associated with age or any other covariate after age adjustment. Association of ER in nonneoplastic tissue and breast cancer status The crude and age-adjusted ORs for the association between ER levels in nonneoplastic tissue and breast can- cer status overall and stratified by study site are shown in Table 2. The crude ORs suggest a positive association between the percentage of cells staining for ER staining in nonneoplastic tissue and breast cancer status in both sites. Age, however, was a strong confounder due to its associa- tion with case status (t-test p < 0.005) and with ER levels. When age was taken into account, the ORs were attenu- ated toward the value. The OR for the uppermost cat- egory of ER (>66% positively staining cells) relative to the lowermost category (<1% cells staining positively) remained elevated (OR = 2.6; 95% confidence interval (CI): 1.1–6.2) but no other OR was significantly different from the null. This was largely due to the influence from the Kingston site. The association between ER and breast cancer status was not different by menopausal status (p- value for interaction = 0.50). Exclusion of cases with car- cinoma in situ only, controls with atypical ductal hyper- plasia, or subjects whose slides contained no TDLUs changed the results for each site very little. When subjects who reported taking exogenous hormones were excluded, the ORs increased slightly for Toronto but were attenuated slightly to the for Kingston. The percentage of nonneoplastic epithelial cells staining positively for ER was not significantly differentially related to ER positive breast cancer status as compared to ER negative breast cancer (p = 0.72), nor was it signifi- cantly differentially related to PR positive breast cancer status as compared to PR negative breast cancer (p = 0.44; results not shown). Note, however, that the number of ER negative cancer cases (n = 55) or PR negative cancer cases (n = 68) in our study was small and the power to detect differences was low. Association of PR in nonneoplastic tissue and breast cancer status The crude and age-adjusted ORs for the association between PR levels in nonneoplastic tissue and breast can- cer status overall and stratified by study site are shown in Table 3. Among subjects from Toronto, the crude ORs sug- gest a slightly inverse association between the percentage of PR staining cells in nonneoplastic tissue and breast can- cer status; this was not observed in the subjects from King- ston. When age was taken into account, the ORs were only slightly attenuated toward the value. The associations did not differ significantly by menopausal status (p-values for interaction ≥ 0.06). Exclusion of cases with carcinoma Table 2: Association between ER in nonneoplastic tissue and breast cancer status, by study site Controls Cases Cells staining for ER (%) Crude OR (95% CI) Age-adjusted OR (95% CI) N 66 79 70 54 37 13 63 66 43 17 11 43 37 28 11 (%) (20.7) (24.8) (21.9) (16.9) (11.6) (4.1) (31.5) (33.0) (21.5) (8.5) (5.5) (37.6) (31.1) (23.5) (9.2) N 23 27 51 40 34 31 21 23 27 17 13 30 23 25 27 (11.2) 1.0 (13.1) 1.0 (0.5–1.9) (24.8) 2.1 (1.2–3.8) (19.4) 2.1 (1.1–4.0) (16.5) 2.6 (1.4–5.1) (15.0) 6.8 (3.1–15.3) (20.8) 1.0 (22.8) 1.0 (0.5–2.1) (26.7) 1.9 (0.9–3.8) (16.8) 3.0 (1.3–6.9) (12.9) 3.5 (1.4–9.1) (28.6) 1.0 (21.9) 0.9 (0.4–1.8) (23.8) 1.3 (0.6–2.6) (25.7) 3.5 (1.5–8.2) Site Both <1% 1–5 6–10 11–33 34–66 >66 Toronto <1% 1–5 6–10 11–33 >33 Kingston ≤10% 11–33 34–66 >66 CI, confidence interval; ER, estrogen receptors; OR, odds ratio. 1.0 0.9 (0.5–1.7) 1.5 (0.8–2.8) 1.3 (0.7–2.5) 1.4 (0.7–2.8) 2.6 (1.1–6.2) 1.0 0.9 (0.5–2.0) 1.2 (0.6–2.5) 1.4 (0.6–3.6) 1.4 (0.5–3.9) 1.0 0.9 (0.4–1.7) 1.1 (0.5–2.4) 2.7 (1.1–6.6) Page 5 of 9 (page number not for citation purposes)