Article | Howsam et al. trend using the categorized variable as quanti- tative after assigning codes 1 to 3 to each cate- gory deﬁned by tertiles. Interactions between exposures and genetic alterations in tumors were tested with logistic regression models com- paring cases with the alteration to cases without it. All p-values calculated were two sided. Results Characteristics of cases and controls are shown in Table 1. Sex, age, and energy intake were used as frequency-matching criteria. BMI estimated 10 years before diagnosis was not related to disease. In contrast, BMI at diagnosis was inversely related to disease, probably due to cancer-related weight loss, although no association was found between plasma lipids and disease, or between plasma Table 1. Population characteristics. lipids and OC concentrations. In this popula- tion, alcohol intake, but not smoking, was a strong risk factor for colorectal cancer, both in duration and in average daily consumption. NSAIDs other than aspirin were protective but not signiﬁcantly so. OC levels. Lipid-corrected concentrations of OCs are shown in Table 2. The most abun- dant compound was p,p´-DDE, followed by HCB and β-HCH. Summed PCB concentra- tions were similar to those of β-HCH. The proportions of samples with values lower than LODs are also shown in Table 2. PCB-28 and PCB-52 were detected in only a small proportion of cases, although the LOD was very low. These compounds are more easily metabolized than are other PCBs because of the arrangement of their chlorine atoms and Controls No. (%) 43 (57) 33 (43) 26 (34) 25 (33) 25 (33) 24 (32) 26 (34) 26 (34) 24 (32) 33 (43) 19 (25) 19 (25) 42 (55) 15 (20) 26 (34) 21 (28) 29 (38) 34 (45) 19 (25) 23 (30) 36 (47) 35 (46) 5 (6) 9 (20) 23 (53) 11 (25) 9 (21) 20 (47) 14 (33) 6 (18) 20 (61) 7 (21) 52 (68) 12 (15) 12 (15) Cases No. (%) 75 (57) 57 (43) 46 (35) 47 (36) 39 (30) 46 (35) 43 (33) 43 (33) 56 (42) 51 (39) 25 (19) 42 (32) 57 (43) 33 (25) 44 (33) 48 (36) 40 (30) 42 (32) 38 (29) 52 (39) 42 (31) 66 (50) 24 (18) 20 (26) 37 (49) 18 (24) 20 (27) 22 (29) 33 (44) 16 (28) 25 (44) 16 (28) 101 (76) 22 (16) 9 (6) OR (95% CI) 1.00 1.07 (0.60–1.92) 1.00 1.09 (0.54–2.20) 0.91 (0.45–1.83) 1.00 0.82 (0.39–1.73) 0.83 (0.38–1.82) 1.00 0.65 (0.34–1.25) 0.53 (0.24–1.17) 1.00 0.61 (0.31–1.20) 0.95 (0.41–2.18) 1.00 1.37 (0.67–2.81) 0.79 (0.39–1.57) 1.00 2.22 (0.93–5.30) 2.40 (1.02–5.63) 1.00 2.42 (1.13–5.17) 7.39 (2.13–25.7) 1.00 0.75 (0.29–2.00) 0.66 (0.21–2.12) 1.00 0.48 (0.17–1.36) 1.05 (0.38–2.96) 1.00 0.55 (0.17–1.76) 1.25 (0.31–5.11) 1.00 0.92 (0.42–2.04) 0.43 (0.16–1.11) p-Valuea 0.09 0.79 0.49 0.05 0.001 0.47 0.81 0.78 0.12 Sex Male Female Age (years) 24–63 63–73 73–92 Energy intake (calories/day) 663–1,733 1,733–2,280 2,280–4,418 BMI 16.8–25.0 25.0–30.0 30.0–40.7 BMI 10 years before diagnosis 17.6–25.0 25.0–30.0 30.0–43.1 Plasma lipids (g/L) 2.58–4.94 4.94–5.85 5.85–9.55 Alcohol duration (years) 0 1–40 40–74 Alcohol consumption (g/day) 0 1–60 60–410 Tobacco use (menb) Nonsmoker Ex-smoker Smoker Smoking duration (years, menb) 0 1–40 40–79 Parity (women) 0–2 2–4 4–9 NSAID use None Aspirin Other 1462 aTest for linear trend adjusted for age, sex, energy intake, and BMI. bOnly 6% of women ever smoked in this population. VOLUME 112 | NUMBER 15 | November 2004 • Environmental Health Perspectives their lower degree of chlorination (Borlakoglu and Walker 1989). δ-HCH was not detected in any individual, and although Pe-CB and PCB-101 were detected in a few samples, their LODs were higher than other OCs; these three compounds were therefore excluded from statistical analyses. Compounds were divided into two groups according to water solubility, and cases had slightly higher levels than did controls of both groups (data not shown). PCBs were grouped according to their structure, which is related to toxicity (ATSDR 2000; Safe 1990). Mono- ortho PCBs 28 and 118 have a relatively “planar” configuration compared with the remaining, di-ortho PCBs measured here. Exposure to mono-ortho PCBs 28 and 118 was almost double in cases compared with controls, whereas exposure to di-ortho PCBs was only slightly higher for cases than for controls. OC levels and colorectal cancer risk. Table 3 shows median lipid-corrected concen- trations and 5th and 95th percentiles for each compound, separated for cases and controls. ORs for the association of OCs with colorectal cancer, adjusted for age, sex, BMI, and energy Table 2. Lipid-corrected serum concentrations of OCs. Mediana (cutpoints)b 3,686 (2,574–5,565) 444 (336–740) 1,753 (1,344–2,522) 17 (< 2.8–30) 1,057 (779–1,422) 10 (< 1.5–46) < 3.5 (< 3.5) 92 (< 21.0–127) < 4.6 (< 4.6) 362 (255–487) 308 (245–404) 252 (190–333) LODc 0.2 1.5 77.9 2.8 34.4 1.5 3.5 21.0 4.6 16.0 15.3 16.0 Percent of samples > LODd 100 100 98 61 100 56 25 62 9 100 98 98 OC p,p´-DDE p,p´-DDT HCB α-HCH β-HCH γ-HCH PCB-28 PCB-118 PCB-52 PCB-153 PCB-138 PCB-180 OC p,p´-DDE p,p´-DDT HCB α-HCH β-HCH γ-HCH PCB-28 PCB-118 PCB-52 PCB-153 PCB-138 PCB-180 aLipid-corrected concentrations expressed as ng/g lipid. bCutpoints were 33rd and 66th percentiles, except for com- pounds for which the 33rd percentile was < LOD, in which case median of measured values were used. cLipid cor- rected (ng/g lipid) using average lipid concentration in the population (5.44 g lipid/L serum). dProportion of samples with values > LOD. Table 3. Lipid-corrected serum concentrations [median (5th–95th percentile); ng/g lipid] of OCs in cases and controls. Cases 3,936 (600–11,804) 396 (124–2,077) 1,753 (487–5,777) 21 (< 2.8–94) 1,042 (315–2,971) 10 (< 1.5–121) < 3.5 (< 3.5–228) 103 (< 21–319) < 4.6 (< 4.6–49) 381 (118–1,018) 327 (121–992) 259 (87–741) Controls 2,977 (611–13,608) 609 (137–3,848) 1,763 (720–4,848) 14 (< 2.8–55) 1,119 (345–3,654) 10 (< 1.5–399) < 3.5 (< 3.5–43) 63 (< 21–404) < 4.6 (< 4.6–< 4.6) 340 (118–917) 301 (91–830) 238 (72–650)