International Agency for Research on Cancer (IARC) - Summaries & Evaluations
VOL.: 6 (1974) (p. 87)
5. Summary of Data Reported and Evaluation
(N.B.: This section should be read in conjunction with the section
'General Conclusions on Hormones'.)
5.1 Animal carcinogenicity data
Mestranol was tested in mice and rats by the oral route; in most
studies it was administered in combination with progestins. When
administered alone, the incidences of pituitary tumours were increased
in both sexes of one strain of mice, and malignant mammary tumours
were produced in males and females of another strain. It also produced
an increased incidence of mammary tumours in castrated male mice and
of malignant mammary tumours in female rats.
In experiments where mestranol was administered to female mice in
combination with norethynodrel (as Enovid), pituitary, mammary,
vaginal and cervical tumours were produced. In rats, combinations with
norethynodrel and norethisterone produced an excess of benign
liver-cell tumours in male rats and increased the incidence of
malignant mammary tumours in rats of both sexes.
The results in dogs and monkeys were difficult to assess since the
studies were still in progress at the time of reporting.
5.2 Human carcinogenicity data
No case reports or epidemiological studies on the effects of mestranol
alone were available to the Working Group. Epidemiological studies on
steroid hormones in oestrogen-progestin contraceptive preparations
have been summarized in the section "Oestrogens and Progestins in
Relation to Human Cancer" in this volume.
Subsequent evaluations: Vol. 21 (1979);
Suppl. 7 (1987)
Last updated: 18 March 1998