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

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