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IT is known that epidermal mitosis is stimulated by androgens (Montagna, Kenyon and Hamilton, 1949) and also by oestrogens (Bullough and van Oordt, 1950). These hormones may, therefore, be expected to promote the rate of skin tumour development by chemical carcinogens provided there is no antagonism between the hormones and the particular carcinogen concerned. However, on the basis of studies of the effect of methylcholanthrene on mouse vagina and seminal vesicle, Jackson and Robson (1957) have suggested that this carcinogen may affect the metabolism of steroid hormones, possibly by a competitive antagonism. Hamer and Marchant (1957) found a sex difference in the amount of collagen in mouse skin. Methylcholanthrene painting made the collagen compositions of male and female mouse skins approach each other, and this would be compatible with a hypothesis of antagonism. Jull (1956) suggests that methylcholanthrene has a progesterone-mimetic effect on mouse breast tissue, but he indicates that oestrogen may be an essential synergist in the induction of breast tumours with this carcinogen. At the time when oestrogens had been proved to be important aetiological factors in the experimental production of breast tumours, a few studies were made on the influence of these hormones on skin tumour induction by tar and various carcinogens. The results were somewhat conflicting and may have been influenced by the particular carcinogen used. Gilmour (1937) found the carcinogenic response of the skin to benzpyrene paintings was increased by treatment of both males and females with oestrone. More oestrogen-treated mice than controls developed tumours and they tended to appear earlier. Perry and Ginzton (1937) compared the development of skin tumours in intact and spayed female mice painted with 1: 2: 5: 6-dibenzanthracene, with and without simultaneous oestrone treatment. They encountered a heavy mortality, but were of the opinion that the incidence of skin tumours was not affected by spaying or oestrone treatment. Paletta and Max (1942) studied the influence of oestradiol treatment of intact female mice on the induction of skin tumours with methylcholanthrene. They found that papil-lomas appeared at about the same time in oestrogen-treated and control mice, but the time required for transformation to malignant tumours was reduced significantly by 1-8 weeks. Recently there have been indications that a different yield of skin tumours may be obtained in the two sexes after treatment with chemical carcinogens and promoting agents. Salaman and Roe (1956) found that treatment with 9:10-dimethyl-1 2-benzanthracene followed by croton …

The Influence of Sex and Castration on the Induction of Skin Tumours in Mice by Methylcholanthrene