Abstract
The production of breast tumors in non-susceptible female mice of strains IF, CBA, JK, and NH by subcutaneous injection of methylcholanthrene was reported almost simultaneously in England 1 and in this country. 2 Observations in this laboratory also indicate that methylcholanthrene may affect the production of mammary carcinoma in a strain of mice that is known to develop the tumors spontaneously.
Breeding female dilute brown (Little dba) mice have a high incidence of spontaneous mammary carcinoma. 3 Subline 212, on which our experiments were performed, has a lower incidence of breast tumors than other members of the strain. Forty-two identified breeding female mice of this line have been observed for at least one year. Fourteen of them developed one or more spontaneous breast tumors when 250 to 475 days old. The average latent period was 371.0 days.
Most dilute brown mice died of leukosis if they were painted with methylcholanthrene solutions. 4 The carcinogen was applied to the unepilated skin twice weekly with a No. 6 camel's hair brush. The site was changed with each painting in the following order: head, left hind leg, right hind leg, left foreleg, right foreleg, sacral region, abdomen, interscapular region, anterior thorax. None of the male mice that were painted developed breast tumors. Thirteen of 65 breeding females of line 212 that were treated with methylcholanthrene had one or more mammary carcinomata. (Table I.) They appeared between the 106th and 268th day of life. The average latent period for these tumors was 181.3 days. The duration of painting varied. No breast cancer was found among 75 virgin females that were treated similarly.
The gross and microscopic appearance of the breast tumors was characteristic.
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