Do Polychlorinated Biphenyls Cause Malignant Melanoma after Occupational Exposure?

1. Cohort studies cited in both IARC Monograph and meta-analysis by Boffetta et al. have relative risks close to one.


 Relative Risk (C.I.)

 # Cases/Deaths

 Exposure Period

 Follow-Up Period


De Guire et al. (1988)

 2.70 (1.31-4.09)

 10 (incidence)




Tynes et al. (1994)

 1.12 (0.67-1.57)

 19 (incidence)




Loomis et al. (1997)

 1.04 (0.86-1.22)

 116 (mortality)




Yassi et al. (2003)

 2.20 (1.05-3.35)

 10 (incidence)




Mallin et al. (2004)

 0.97 (0.16-1.78)

 2 (mortality)




Peastori et al. (2013)

 0.50 (0.01-0.99)

 1 (mortality)




Ruder et al. (2014)

 1.20 (0.88-1.52)

 47 (mortality)




“ . . . in our meta-analysis, the summary risk estimates for MM [malignant melanoma] are close to one in both general-population studies and occupational cohorts.” [Boffetta et al., p. 68]

Note that 5 of the 7 studies are not statistically significant (confidence interval includes < 1.0.) “. . . a result that is not statistically significant does not mean that chance is responsible for the results—only that it cannot be excluded as a likely explanation.” [Hennekens, p. 33]

Industrial abbreviations: TW = telecommunication workers; EW = electrical workers; TCW = transformer and capacitor workers;

2. No mention of a link between PCBs and melanoma are found in standard references. 

The association is not mentioned in Cecil Medicine, Preventing Occupational Disease and Injury, or Textbook of Clinical Occupational and Environmental Medicine. [Cecil, APHA, Rosenstock] ACGIH classifies PCB 1254 as A3, Confirmed Animal Carcinogen with Unknown Relevance to Humans. (“Available evidence does not suggest that the agent is likely to cause cancer in humans except under uncommon or unlikely routes or levels of exposure.”) [Guide to Occupational Exposure Values] Likewise, no mention was made in the following abstracts: 

Occupational exposure to polychlorinated biphenyls and cancer risk

A cohort study of Swedish capacitor manufacturing workers exposed to polychlorinated biphenyls (PCBs)

Weight of evidence evaluation of potential human cancer risks from exposure to polychlorinated biphenyls: an update based on studies published since 2003

Polychlorinated biphenyls and cancer: an epidemiological assessment

A case-control study of cancer mortality at a transformer-assembly facility

Cancer Incidence and mortality in workers employed at a transformer manufacturing plant: update to a cohort study

Update of the mortality study of workers exposed to polychlorinated biphenyls (Pcbs) in two Italian capacitor manufacturing plants

3. People with increased serum levels of PCBs do not have increased risk of melanoma.

“Yusho” and “Yucheng” Asian populations who ate cooking oil contaminated with PCBs did not have increased melanoma. [Li et al. 2015]

Referring to Yusho and Yucheng patients, “Exposed people had blood PCB concentrations that were 100 to 1000 times higher than in the non-exposed population.” [IARC Monograph 107, p. 424]

The NHANES geometic mean = 3.31 ng/g lipid for PCB 156. NHANES "generates biomonitoring reference ranges for the general US population." [LaDou, p. 721, 716] A ng is 1 billionth of a gram. 3 ng/g = 3 ppb.

“PCB concentrations in the adipose tissue of Yusho patients were estimated to have reached 46-47 ppm . . . “[Li et al. 2015]

“Gallagher et al. (2011) conducted a case– control study of 80 patients with malignant melanoma of the skin and 310 controls. The cases were part of a larger case–control study and were originally recruited to evaluate the effect of exposure to ultraviolet (UV) light and gene variants on risk of melanoma, and the controls were recruited using population-based registries. Lipid-adjusted plasma concentrations of 14 PCB congeners were determined and data were reported for 8, as well as for total PCBs, and dioxin-like and non-dioxin-like PCBs. Statistically significant associations with malignant melanoma were observed for the highest compared with the lowest quartile for: total PCBs (OR, 6.02; 95% CI, 2.0–18.17); . . . The Working Group considered that, in light of its appropriate design and control of relevant potential confounders, this was a high-quality study, despite the relatively small sample size and being described as “preliminary” by the authors.” [IARC Monograph 107, p. 246]

“Finally, since blood specimens for CMM [cutaneous malignant melanoma] cases were collected after disease development, there is a possibility that the disease process or its treatment may have affected plasma levels of OCCs [organochlorine compounds]. It is known that weight loss due to chemotherapy may lead to increases in plasma levels as the bioaccumulated OCCs stored in fat are mobilized.” [Gallagher, p. 1879]

“Studies of diet and melanoma have—for the most part—not found consistent differences between melanoma cases and controls for dietary intake of foods known to carry high levels of PCBs.” [Gallagher, p. 1875]