The influence of ionizing radiation and 7,12-dimethylbenz(a)anthracene on the expression of mammary ductal dysplasia in mice

These studies were undertaken to determine if altered growth potential of mammary epithelial cells could be detected in outgrowths derived from monodispersed mammary cells of virgin female BALB/c mice previously exposed to ionizing radiation or 7,12-dimethylbenz(a)anthracene (DMBA).

Monodispersed mammary cells were obtained by enzymatic dissociation of mammary tissues of 12-week-old virgin female BALB/c mice. Twenty-four hours prior to cell dissociation, donor animals were exposed to either γ-ray irradiation or DMBA, while control donors were untreated. Mammary outgrowths were then derived from the donor cells by injecting either 10⁵ or 10⁴ cells into the gland free mammary fat pads of three-week-old virgin female BALB/c mice. In the initial studies all outgrowths were removed 10 weeks after injection of cells. The outgrowths that resulted were examined at the whole mount and histological level and were classified as having a normal ductal architecture or as having ductal dysplasia or alveolar adenosis. Outgrowths exhibiting ductal dysplasia were further classified as having mild or severe epithelial hyperplasia. The data indicated that treatment of donor animals with either γ-radiation or DMBA could result in an increased incidence of ductal dysplasias over control levels. Further, the incidence of lesions observed in all groups was influenced by the number of cells used to derive the outgrowths in that lesions were more frequent in outgrowths derived from 10⁴ rather than 10⁵ cells.

The findings of these experiments indicate that acquisition of altered growth potential by mammary cells that results in expression of ductal dysplasia occurs soon after carcinogen treatment and that deriving mammary outgrowths from dissociated cells results in enhanced expression of these lesions.