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III.
CARCINOGENIC EFFECTS
Human Studies
The evidence for the human carcinogenicity of PCBs has been determined by IARC (1987) to be
limited, due to concurrent exposures of test subjects to other chemicals, and to the small numbers of
individuals examined. A study of workers heavily exposed to Aroclor 1254 (54% chlorine, by weight)
for 9 years, showed 2 out of 31 heavily exposed workers developed malignant melanoma, while 1 out
of 41 less heavily exposed workers developed this tumor (Bahn et al., 1976; 1977). The expected
number of melanomas in a population this size was 0.04. IARC (1978) concluded that there was
suggestive evidence of carcinogenicity in humans.
Brown and Jones (1981) and Brown (1987) found an increase in the mortality caused by liver or biliary
passage cancer (5 observed, 1.9 expected) in 2567 US workers exposed to Aroclor 1254 during the
manufacture of capacitors. Four of the 5 deceased workers were female.
Bertazzi et al. (1982) reported on a study of capacitor manufacturing workers in Italy. Workers were
exposed to mixtures of PCB congeners containing 54% chlorine prior to 1964, and 42% chlorine after
that time. In these workers, significant increases in the incidence of cancers of the digestive, lymphatic,
and hematopoietic systems were observed in both male and female workers. An expanded study was
later conducted by Bertazzi et al. (1987) who recorded cancer mortality in 2100 male and female
workers from 1946 to 1982. Cancers of the gastrointestinal tract were significantly increased in male
workers (6 observed, 2.2 expected) and hematopoietic cancers were significantly increased in female
workers (4 observed, 1.1 expected).
PCB content in human fat tissues has been correlated with the occurrence of stomach, colon, pancreas,
ovary, and prostate cancers (Unger et al., 1982; 1984).
A large population of people in Japan were exposed to PCBs from contaminated cooking oil (Umeda,
1984). In these patients, a 5-fold increase in liver cancer was reported, but a dose-response was not
established. In a cohort of 887 male intoxicated patients with “Yusho” disease, Kuratsune et al. (1986)
found an increase in mortality from malignant tumors (33 observed, 15.5 expected). Deaths from
malignant liver and lung tumors were particularly high (9 observed, 1.6 expected; 8 observed, 2.5
expected, respectively). Female Yusho patients (n = 874) did not show the increase in cancer
mortality.
Animal Studies
Early studies by Kimura and Baba (1973) and Ito et al. (1974) did not demonstrate carcinogenicity of
PCBs in male or female rats orally exposed to highly chlorinated (60% by weight) PCBs in the diet for
up to 77 weeks. In this study, 20 rats (10/sex) were exposed to diets ranging from 38.5 to 462 ppm
PCBs. Ten rats (5/sex) served as experimental controls. Each rat was exposed to a unique treatment
regimen that differed by amount of PCB ingested and duration of exposure. Female rats exhibited
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