IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

Case reports
2. Studies of Cancer in Humans
A cluster of cancer cases in a naphthalene purification plant was reported in the
former East Germany (Wolf, 1976, 1978). This plant operated between 1917 and 1968
and a total of 15 employees were reported to have worked in this unit of the plant during
the preceding 20–30 years. Seven employees were diagnosed with cancer, including four
cases of laryngeal cancer. Diagnosis was established between 1964 and 1973 and the age
at diagnosis was 60–71 years. The incidence rate for laryngeal cancer in the former East
Germany in 1970 was given as 6.3 per 100 000. The four workers had been exposed for
7–31 years. The limit value for exposure to naphthalene at that time was 20 mg/m 3 , with
peak values of 50 mg/m 3 . Concomitant exposure to various tar products was mentioned.
All four cases were reported to have been smokers. [The Working Group noted that no
inference on the carcinogenicity of naphthalene can be drawn from these observations.]
Ajao et al. (1988) reported on 23 consecutive cases of colorectal carcinoma admitted
during June 1982 and May 1984 to a university college hospital in Nigeria. Eleven of
these patients were 30 years or younger at diagnosis. Based on family history, proctosigmoidoscopy,
barium enema and autopsy, no indication of familial polyposis among
these cases was ascertained. Half of the patients mentioned a history of taking Kafura, a
local indigenous treatment for anorectal problems, which contains naphthalene. The
other half of the patients did not know whether they had been given Kafura during early
childhood. [The Working Group noted that no inference on the carcinogenicity of
naphthalene can be drawn from these observations.]
3. Studies of Cancer in Experimental Animals
3.1 Oral administration
NAPHTHALENE 385
Rat: A group of 28 BD I and BD III rats [sex and number of each strain not specified],
about 100 days old, was fed a diet [not specified] containing naphthalene (spectrographically
pure) in oil [type unspecified] at a dose of 10–20 mg per day on six days per
week, for 100 weeks. Animals were kept under observation until they died. The average
life expectancy was 800 days, which was said to be similar to that of control rats [no
details were provided regarding control animals]. All animals were subjected to necropsy
with histopathological examination of abnormal tissues only. No tumours were found in
any of the rats examined. (Schmähl, 1955). [The Working Group noted the small number
of animals used and the incomplete reporting of this study.]