Exposure assessment to polycyclic aromatic hydrocarbons and breast cancer risk stratified by (first-degree) family history of breast cancer*
| Exposure assessment | No family history | (First-degree) family history | p-interaction | ||||||
| Cases (%) | Controls (%) | OR | 95% CI | Cases (%) | Controls (%) | OR | 95% CI | ||
| Ever-never: any level | |||||||||
| Never | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Ever | 594 (68.0) | 597 (61.0) | 1.23 | 1.01 to 1.51 | 155 (71.4) | 90 (55.2) | 1.84 | 1.16 to 2.92 | |
| Ever-never: at maximum level† | |||||||||
| Never | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Maximum level at low‡ | 76 (08.7) | 92 (09.4) | 1.04 | 0.73 to 1.48 | 14 (06.4) | 15 (09.2) | 0.95 | 0.40 to 2.24 | |
| Maximum level at medium§ | 131 (15.0) | 150 (15.3) | 1.16 | 0.87 to 1.56 | 44 (20.3) | 28 (17.2) | 1.68 | 0.90 to 3.13 | |
| Maximum level at high¶ | 387 (44.3) | 355 (36.3) | 1.31 | 1.04 to 1.64 | 97 (44.7) | 47 (28.8) | 2.27 | 1.34 to 3.86 | |
| Ptrend=0.02 | Ptrend<0.01 | Pint-trend=0.03 | |||||||
| Duration (years) of exposure at any level | |||||||||
| None (0) | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Short (0.1–4.2) | 178 (20.4) | 194 (19.8) | 1.31 | 1.01 to 1.71 | 57 (26.2) | 35 (21.5) | 1.95 | 1.09 to 3.48 | |
| Moderate (4.3–13.0) | 202 (23.1) | 202 (20.7) | 1.22 | 0.94 to 1.59 | 54 (24.9) | 28 (17.2) | 2.16 | 1.17 to 3.97 | |
| Long (13.1–82.2) | 214 (24.5) | 201 (20.5) | 1.15 | 0.88 to 1.50 | 44 (20.3) | 27 (16.5) | 1.38 | 0.72 to 2.65 | |
| Ptrend>0.2 | Ptrend>0.1 | Pint-trend>0.2 | |||||||
| Duration (years) of exposure at medium§ or high¶ levels | |||||||||
| None (0) | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Ever: maximum at low level** | 76 (08.7) | 92 (09.4) | 1.04 | 0.73 to 1.47 | 14 (06.4) | 15 (09.2) | 0.97 | 0.41 to 2.28 | |
| Short (0.1–2.7) | 159 (18.2) | 163 (16.6) | 1.36 | 1.03 to 1.80 | 44 (20.3) | 31 (19.0) | 1.64 | 0.90 to 3.00 | |
| Moderate (2.8–9.0) | 152 (17.4) | 169 (17.3) | 1.14 | 0.86 to 1.51 | 51 (23.5) | 27 (16.6) | 2.24 | 1.20 to 4.18 | |
| Long (9.1–80.8) | 207 (23.7) | 173 (17.7) | 1.29 | 0.98 to 1.70 | 46 (21.2) | 17 (10.4) | 2.53 | 1.24 to 5.16 | |
| Ptrend=0.09 | Ptrend<0.01 | Pint-trend=0.01 | |||||||
| Duration (years) of exposure at the high level¶ | |||||||||
| None (0) | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Ever: maximum at low‡ or medium§ levels‡‡ | 207 (23.7) | 242 (24.7) | 1.11 | 0.86 to 1.43 | 58 (26.7) | 43 (26.4) | 1.43 | 0.82 to 2.49 | |
| Short (0.1–2.3) | 121 (13.8) | 114 (11.6) | 1.50 | 1.10 to 2.05 | 35 (16.1) | 20 (12.3) | 1.94 | 0.98 to 3.82 | |
| Moderate (2.4–7.4) | 109 (12.5) | 118 (12.1) | 1.15 | 0.83 to 1.58 | 27 (12.5) | 16 (09.8) | 2.31 | 1.07 to 5.01 | |
| Long (7.5–74.1) | 157 (18.0) | 123 (12.6) | 1.29 | 0.95 to 1.75 | 35 (16.1) | 11 (06.7) | 2.79 | 1.25 to 6.24 | |
| Ptrend>0.1 | Ptrend<0.01 | Pint-trend=0.03 | |||||||
| Weighted duration (years)—equation (1) | |||||||||
| None (0) | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Short (0.1–0.4) | 181 (20.7) | 193 (19.7) | 1.25 | 0.96 to 1.63 | 53 (24.4) | 36 (22.1) | 1.66 | 0.94 to 2.94 | |
| Moderate (0.5–1.7) | 287 (21.4) | 201 (20.5) | 1.18 | 0.90 to 1.53 | 46 (21.2) | 28 (17.2) | 1.75 | 0.95 to 3.25 | |
| Long (1.8–55.1) | 226 (25.9) | 203 (20.8) | 1.25 | 0.97 to 1.63 | 56 (25.8) | 26 (15.9) | 2.26 | 1.19 to 4.28 | |
| Ptrend>0.1 | Ptrend<0.01 | Pint-trend=0.06 | |||||||
| Average probability—equation (2) | |||||||||
| None (0) | 280 (32.0) | 381 (39.0) | ----- | 62 (28.6) | 73 (44.8) | ----- | |||
| Low (0.01–0.02) | 165 (18.9) | 191 (19.5) | 1.18 | 0.90 to 1.55 | 53 (24.4) | 38 (23.3) | 1.57 | 0.89 to 2.76 | |
| Medium (0.03–0.07) | 212 (24.3) | 202 (20.6) | 1.36 | 1.05 to 1.76 | 43 (19.8) | 27 (16.6) | 1.71 | 0.91 to 3.20 | |
| High (0.08–0.88) | 217 (24.8) | 204 (20.9) | 1.14 | 0.87 to 1.49 | 59 (27.2) | 25 (15.3) | 2.55 | 1.34 to 4.84 | |
| Ptrend>0.1 | Ptrend<0.01 | Pint-trend=0.03 | |||||||
The bold indicates the categories that are significant at alpha = 0.05.
*Adjusted for age, centre, education, ethnicity, smoking (pack-years). All p trend values are calculated by treating ordinal categories as continuous values.
†Maximum level classification, regardless of duration, is the maximum exposure level to which the participant was exposed across all occupations.
‡Analysis for exposure at low level (estimated probability of exposure above 0.2 mg/m3 of coal tar pitch volatiles) is θ=(0.1%–2.9%) in at least one job.
§Analysis for exposure at medium level (estimated probability of exposure above 0.2 mg/m3 of coal tar pitch volatiles) is θ=(3.0%–8.9%) in at least one job.
¶Analysis for exposure at high level (estimated probability of exposure above 0.2 mg/m3 of coal tar pitch volatiles) is θ≥9% in at least one job.
**To ensure referent group are truly unexposed, a nuisance variable was created for the low-exposed group where value=1, if highest duration at low level exposure, else 0.
‡‡ To ensure referent group are truly unexposed, a nuisance variable was created for the low-exposed/medium-exposed group where value=1, if highest duration at low or medium level exposure, else 0.