Administration of estrogen and of cortisol for 1 month to 2½-month-old female C3H/He Crgl mice resulted in variable degrees of lobuloalveolar development. The localized alveolar hyperplasias are referred to as “noduloids” solely on morphologic grounds, and they are without known precancerous significance. Some “noduloids” are also seen after estrogen and after cortisol treatment of mice freed of the mammary tumor agent.

Month-long treatment of 3-month-old mice with estrogen or with mammotropin resulted in significantly increased incidences of nodules at 6 months of age. This was not seen after month-long cortisol or deoxycorticosterone treatments. Continuous treatment of 3-month-old mice for 3 months with estrogen resulted in mammary glands with numerous nodules and “noduloids.” The continuity in morphology between these structures is emphasized.

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Assisted by research grants from the American Cancer Society (MOR-27 and E-11) and by University of California Cancer Research funds.

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