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

(Group 3)

For definition of Groups, see Preamble Evaluation.

Supplement 7: (1987) (p. 348)

CAS No.: 723-46-6
Chem. Abstr. Name: Benzenesulfonamide, 4-amino-N-(5-methyl-3-isoxazolyl)-

A. Evidence for carcinogenicity to humans (inadequate)

Although no increase in the incidence of cancer at all sites combined was noted during 1969-1976 among 1709 members of a prepaid health plan prescribed sulfamethoxazole during 1969-1973, significant increases in the incidence of nasopharyngeal carcinoma (3 observed, 0.1 expected; relative risk, 30.0 [95% confidence interval, 23.7-36.3]) and of cancer of the cervix after a two-year lag period (7 observed, 2.2 expected; relative risk, 3.2 [1.8-4.5]) were observed. However, a significant deficit of colon cancer was also seen (none observed, 4.7 expected) [ref: 1].

B. Evidence for carcinogenicity to animals (limited)

Sulfamethoxazole produced thyroid tumours in rats following its oral administration; no information on other tumour types was reported [ref: 2].

C. Other relevant data

In a single study, sulfamethoxazole did not induce chromosomal aberrations in human lymphocytes in vivo or in vitro. It was not mutagenic to bacteria [ref: 3].

Overall evaluation

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

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Vol. 79 (2001)

Also see previous evaluation: Vol. 24 (1980)


1. Friedman, G.D. & Ury, H.K. (1980) Initial screening for carcinogenicity of commonly used drugs. J. natl Cancer Inst., 65, 723-733

2. IARC Monographs, 24, 285-295, 1980

3. IARC Monographs, Suppl. 6, 502-503, 1987


Last updated: 11 March 1998

    See Also:
       Toxicological Abbreviations
       Sulfamethoxazole  (IARC Summary & Evaluation, Volume 24, 1980)
       Sulfamethoxazole  (IARC Summary & Evaluation, Volume 79, 2001)