Detection of inapparent nodule-transformed cells in the mammary gland tissues of virgin female BALB/cfC3H mice.

Inapparent nodule-transformed cells were recovered from morphologically normal mammary tissue from virgin female BALB/cfC3H/Crgl (mouse mammary tumor-positive) mice before the appearance of hyperplastic alveolar nodules (HAN) or tumors, by means of the cell dissociation technique. Mammary tissues were dissociated by means of collagenase (0.1%), hyaluronidase (0.1%), and pronase (1.25%). Aliquots of 10(5) viable cells in 0.01 ml medium were injected into the gland-free mammary fat pads of 3-week-old female syngeneic mice. After 10 weeks the outgrowths were examined and classified as ductal, HAN, tumor, or combinations of these types. The presence of HAN outgrowths indicated the presence of nodule-transformed cells in the donor mammary tissues. Nodule-transformed cells were recovered from 2-month-old donors, and the number of HAN outgrowths increased with donor age. Overt HAN and tumors did not appear in virgin female BALB/cfC3H/Crgl mice younger than 8 to 9 months of age. The data suggest that inapparent nodule-transformed cells occurred long before the appearance of HAN of tumors and that the numbers of transformed cells increased with donor age.