Exposure to Trichloroethylene Linked With Increased Risk of Parkinson Disease, Cancer

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The findings were consistent with the chemical's known carcinogenicity and supportive of the emerging preclinical and epidemiological evidence that ties TCE exposure to patients with PD.

Earl Ray Dorsey, MD, the David M. Levy Professor of Neurology at the University of Rochester

Earl Ray Dorsey, MD

Findings from a recently published retrospective study showed elevated rates of Parkinson disease (PD) and trichloroethylene (TCE)-related cancers in attorneys who worked next to a contaminated dry-cleaning site. Although the evidence was circumstantial and not definitive, the investigators concluded that the findings are "concerning," for the role TCE and perchloroethylene (PCE) may be playing.1

TCE and PCE are 6-atom molecules with many uses, including decaffeinating, degreasing, and dry cleaning. Led by Earl Ray Dorsey, MD, the David M. Levy Professor of Neurology at the University of Rochester, 79 of the 82 attorneys invited (96.3%) completed at least 1 phase of the study. Phase 1 surveyed partners who worked at a law firm in the tower (“tower cohort”) for at least 1 year between 1968 and 2001. In phase 2, the tower cohort was evaluated clinically for PD, cancer, and related conditions.

Proxies completed responses for 14 disabled or deceased individuals. In addition to the partners, the study recruited a comparison group of attorneys for phase 2 of the analysis through the local bar association’s newsletter, flyers, and word of mouth. These lawyers were at least 45 years old and had worked for at least 1 year between 1968 and 2001. To determine whether the tower cohort had an increased prevalence of PD or cancer, investigators compared rates observed in the study population to that expected in the general population based on sex and age at either the time of the assessment or the time of death using a binomial test.

Between the tower cohort and comparison group, the baseline characteristics were generally similar, except that the tower cohort was older (69.5 vs 64.9 years) and had more men (89.9% vs 65.3%). Prior to phase 2, 18 (22.0%) attorneys in the tower cohort died. Obtained health information on 15 of these individuals showed that 2 died with PD, 1 with multiple system atrophy and prostate cancer, and 8 others with a TCE-related cancer. In all, 11 (73.3% of the 15 deceased had at least 1 TCE-associated condition.

Four (5.1%) of the participants in the tower cohort had PD based on reports from a proxy and review of medical records (n = 2), report from a proxy and the National Death Index (n = 1), and self-report and clinical evaluation (n = 1). All told, the proportion of PD found in the study was more than expected based on age and sex (1.7%; P = .01), although it did not statistically significantly differ from the comparison group (18.9%; P = .65).

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"Because the study was retrospective, its biggest limitation is the uncertainty of exposure," the study authors wrote. "The time lag between exposure and diagnosis makes environmental studies challenging. In this case, the extent to which vapors entered the tower or garage over 20 years ago is unknown as no testing (to our knowledge) was performed. However, the extent of contamination, the likely flow of chemicals, and an underground tunnel all suggest that vapor intrusion was possible."

In total, 48 of the 64 participants in the tower cohort underwent clinical evaluations, with death (n = 12) and disability (n = 4) as the only reasons that precluded full participation. All told, results showed that the proportion of individuals with possible PD did not differ (19.1%) from the comparison group (18.9%; P = .65). In terms of TCE-related cancers, 15 of the 79 individuals in the tower cohort had a TCE-related cancer vs 4 (5.3%; P = .049) in the comparison group. Among men only, TCE-related cancers still tended to be more frequent.

To the authors knowledge, this study, and a previously published study on Camp Lejeune, were the first to tie possible environmental exposure to PD. Camp Lejeune was a Marine Corps base where water was contaminated with TCE and other volatile organic compounds. Published in JAMA Neurology in 2023, data revealed a higher crude prevalence rate of PD in Camp Lejeune veterans compared with those stationed at Camp Pendleton (0.33% vs 0.21%), a base with uncontaminated water, resulting in a 70% higher rate (OR, 1.70; 95% CI, 1.39-2.07). Notably, residence at Camp Lejeune was associated with a statistically significant increased risk of prodromal risk scores (internal: OR, 1.14 [95% CI, 1.03-1.26]; Movement Disorders Society: OR, 1.18 [95% CI, 1.06-1.32]) and an overall increased PD risk of 14% to 20% among men.2

REFERENCES
1. Dorsey RE, Kinel D, Pawlik ME, et al. Dry-cleaning chemicals and a cluster of Parkinson’s disease and cancer: a retrospective investigation. 2024;39(3):606-613. doi:10.1002/mds.29723
2. Goldman SM, Weaver FM, Stroupe KT, et al. Risk of Parkinson Disease Among Service Members at Marine Corps Base Camp Lejeune. JAMA Neurol. 2023;e231168. doi:10.1001/jamaneurol.2023.1168
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