Table 3.
Selected RR estimates for liver cancer associated with TCE exposure (overall and highest exposure group) from cohort and case-control studies.
| Overall Exposure | Highest TCE Exposure Group | |||||
|---|---|---|---|---|---|---|
| Study | RR (95% CI) | Alternate RR estimates | Exposure Category | RR (95% CI) | Alternate RR estimates | Comments |
| Cohort Studies | ||||||
| Anttila et al. [38] | 1.89 (0.86, 3.59) a | 2.27 (0.74, 5.29) for 155.0 alone | 100+ μmol/L U-TCA b | 2.74 (0.33, 9.88) | None | ICD-7 155.0 + 155.1. SIR. ICD-7 155.0 for highest exposure group. |
| Axelson et al. [37] | 1.41 (0.38, 3.60) | 1.34 (0.36, 3.42) with estimated female contribution to SIR added c | 100+ mg/L U-TCA | 3.7 (0.09, 21) c | Exclude study | ICD-7 155. SIR reported for males only, but there was a small female component to the cohort. No cases were observed in highest exposure group (i.e., >2 years and 100+ U-TCA), so combined with <2 years and 100+ subgroup and estimated female results. |
| Boice et al. [41] | 0.81 (0.45, 1.33) | 0.54 (0.15, 1.38) for potential routine exposure | ≥5 year exposure | 0.94 (0.36, 2.46) | None | ICD-9 155 + 156. Overall SMR for any potential exposure. Highest exposure mortality RR for any potential exposure, adjusted for date of birth, dates 1st and last employed, race, and sex; referent group is workers not exposed to any solvent. |
| Greenland et al. [42] | 0.54 (0.11, 2.63) | None | NA | d | ICD-8 155 + 156. Mortality OR from nested case-control study. | |
| Hansen et al. [39] | 2.1 (0.7, 5.0) c | None | ≥1,080 months × mg/m3 | 1.0 assumed d | ICD-7 155. SIR. Reported high exposure group results for some cancer sites but not liver. | |
| Morgan et al. [43] | 1.48 (0.56, 3.91) | 0.98 (0.36, 2.13) Published SMR | High cumulative exposure score | 1.19 (0.34, 4.16) | 0.98 (0.29, 3.35) for medium/high | ICD-7 155, ICD-8, −9 155 + 156. Overall mortality RR as reported in Morgan et al. [57] RRs adjusted for age and sex. |
| Raaschou-Nielsen et al. [40] | 1.35 (1.03, 1.77) a,c | 1.28 (0.89, 1.80) for ICD-7 155.0 c | ≥5 years | 1.2 (0.7, 1.9) a,c | 1.1 (0.5, 2.1) ICD-7 155.0 (liver only) c | ICD-7 155.0 + 155.1. SIR. |
| Radican et al. [27] | 1.12 (0.57, 2.19) | 1.25 (0.31, 4.97) for ICD-8, −9 155.0 | >25 unit-year | 1.49 (0.67, 3.34) e | None | ICD-8, −9 155 + 156, ICD-10 C22–C24. Mortality HR adjusted for age, sex and race, with workers with no chemical exposures as referent group. |
| Zhao et al. [25]/Boice et al. [26] | 1.28 (0.35, 3.27) | 1.0 assumed for Zhao et al. [25] d | High exposure score | 1.0 assumed for Zhao et al. [25] d | ICD-9 155 + 156. Overall SMR for males from Boice et al. [26] used in lieu of Zhao et al. [25], who do not report liver cancer results. Highest exposure group RR for liver cancer not reported by Zhao et al. [25] or Boice et al. [26]. | |
Observed and expected numbers of cases combined assuming Poisson distribution for ICD codes identified in comments column.
Mean personal trichloroacetic acid in urine. 1 μmol/L = 0.1634 mg/L.
Male and female results combined assuming Poisson distribution. Details of the approach used to estimate the female contribution for Axelson et al. [37] are presented in U.S. EPA [60].
Hansen et al. [39] and Zhao et al. [25] report a RR estimate for highest TCE exposure groups and other cancers, but not liver. A risk estimate of 1.0 is assigned for highest exposure in these studies, and as an alternate overall RR estimate for the Zhao et al. [25] study, which does not report any liver results, to account for potential publication bias. For the SE (of the log RR) estimates for these null values, SE estimates from cancer types that were expected to have similar numbers of cases were generally used (See Appendix C of U.S. EPA [60] for further details). For Greenland et al. [42], a risk of 1.0 is not assumed for highest exposure since only overall results are presented in that study.
Male and female results combined using inverse-variance weighting, as in a fixed-effect meta-analysis.
HR = hazard ratio, ICD = International Classification of Diseases, NA = not available, OR = odds ratio, RR = relative risk, SIR = standardized incidence ratio, SMR = standardized mortality ratio, TCE = trichloroethylene, U-TCA = urinary trichloroacetic acid.