International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 3)

VOL.: 79 (2001) (p. 703)

CAS No.: 62-56-6
Chem. Abstr. Name: Thiourea

5.  Summary of Data Reported and Evaluation

5.1 Exposure data

Thiourea is used in many industrial applications, including as a chemical intermediate or catalyst, in metal processing and plating and in photoprocessing.

5.2 Human carcinogenicity data

No data were available to the Working Group.

5.3 Animal carcinogenicity data

Thiourea has not been tested in a conventional bioassay of carcinogenicity in rodents that would meet present-day standards. In four early studies involving several strains of mice, thyroid hyperplasia but not thyroid tumours was reported after oral administration of thiourea. In several studies in rats given thiourea orally, either a high incidence of thyroid follicular-cell adenomas and carcinomas or increased incidences of hepatocellular adenomas or tumours of the Zymbal or meibomian glands were reported. However, there were deficiencies in each of these studies and no correspondence between studies with respect to tumour site. In five initiation–promotion studies in rats, thiourea promoted thyroid follicular-cell tumours initiated by N-nitrosobis(2-hydroxypropyl)amine.

5.4 Other relevant data

Thiourea is well absorbed and concentrates in the thyroid. It is readily excreted. It can cross the placental barrier. Thiourea acts by inhibiting thyroid peroxidase, resulting in decreased thyroid hormone production and increased proliferation due to an increase in the secretion of thyroid-stimulating hormone. This is the probable basis of the tumorigenic activity of thiourea for the thyroid in experimental animals.

No data were available on reproductive or developmental effects of thiourea in humans. One study in rats showed growth retardation and malformations of the skeleton and nervous system in the offspring of thiourea-treated animals.

Thiourea did not induce gene mutation in bacteria, but mixed results were obtained in assays in mammalian cells. It consistently induced chromosomal recombination in yeast and insects and induced mammalian cell transformation.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of thiourea.

There is limited evidence in experimental animals for the carcinogenicity of thiourea.

Overall evaluation

Thiourea is not classifiable as to its carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.

Previous evaluations: Vol. 7 (1974) (p. 95); Suppl. 7 (1987) (p. 72)


Last updated: 25 September 2001

    See Also:
       Toxicological Abbreviations
       Thiourea (ICSC)
       Thiourea (CICADS 49, 2003)
       Thiourea  (IARC Summary & Evaluation, Volume 7, 1974)