Several studies have demonstrated the carcinogenic potential of polychlorinated biphenyls (PCBs), a group of chemicals produced by Monsanto until 1977. Here is an overview of key studies and findings:
Animal Studies
The National Toxicology Program (NTP) conducted multiple studies exposing female rats to individual PCBs or PCB mixtures. These studies found increased incidences of benign and malignant tumors in the liver, bile duct, lung, oral mucosa, uterus and pancreas after exposure to PCBs 126, 118, or mixtures[1].
A 1998 study by Mayes et al. found that dietary exposure to Aroclor mixtures 1016, 1242, 1254, or 1260 caused liver tumors in female rats. Aroclor 1254 specifically led to an additional type of liver tumor called hepatocholangioma[1].
Human Studies
An Italian cohort study of capacitor manufacturing workers found excess gastrointestinal tumors (including liver) in men and lymphohematopoietic cancers in women exposed occupationally to PCBs[5].
A meta-analysis by Zani et al. in 2017 found some evidence for an association between PCB exposure and increased risk of non-Hodgkin lymphoma, with a summary odds ratio of 1.5 (95% CI: 1.1-1.7)[4].
Agency Classifications
The International Agency for Research on Cancer (IARC) has classified PCBs as „probably carcinogenic to humans“ (Group 2A)[6].
The U.S. Environmental Protection Agency (EPA) concluded in its reassessment that PCBs are probable human carcinogens, based on clear evidence of carcinogenicity in animal studies and concerning findings in human studies[3].
Mechanisms
Some lower chlorinated PCB congeners and their metabolites have been found to have initiating activity in modified Solt-Farber protocols, contradicting earlier assumptions that PCBs lacked initiating potential[6].
PCB-DNA adducts have been observed in cellular systems and animal studies, providing evidence for genotoxic mechanisms[6].
While early studies found PCBs to be non-mutagenic, more recent research has shown that certain PCB metabolites can induce gene mutations, chromosome breaks, and other genetic damage in vitro and in vivo[6].
In conclusion, while some inconsistencies remain, there is substantial evidence from animal and human studies supporting the carcinogenic potential of PCBs, particularly for liver cancer and non-Hodgkin lymphoma. The mechanisms likely involve both genotoxic and non-genotoxic pathways.
Sources:
[1] [PDF] Report on Carcinogens, Fifteenth Edition – Polychlorinated Biphenyls https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/polychlorinatedbiphenyls.pdf
[2] Polychlorinated biphenyl – Wikipedia https://en.wikipedia.org/wiki/Polychlorinated_biphenyl
[3] Learn about Polychlorinated Biphenyls | US EPA https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls
[4] Polychlorinated biphenyls and cancer: an epidemiological assessment https://pubmed.ncbi.nlm.nih.gov/23672403/
[5] Polychlorinated Biphenyls https://www.ncbi.nlm.nih.gov/books/NBK590799/
[6] Polychlorinated Biphenyl (PCB) carcinogenicity with special … – NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3113507/
[7] Do polychlorinated biphenyls cause cancer? A systematic review … https://www.sciencedirect.com/science/article/abs/pii/S0045653517307555
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