Factors Influencing Expression of Mammary Ductal Dysplasia in Cell Dissociation-derived Murine Mammary Outgrowths

The expression of mammary ductal dysplasia has been shown to be enhanced in mammary outgrowths derived from enzymatically dissociated mammary cells and influenced by the number of cells used to derive the outgrowths. The present study was designed to examine this cell dose effect further and to determine if the developmental state of the outgrowths or the time between carcinogen administration and cell dissociation affects the expression and persistence of the ductal dysplasias. Mammary outgrowths were derived by injecting 104 or 105 enzymatically dissociated mammary cells into gland-free fat pads of 3-week-old female BALB/c mice. Donor animals were untreated or were exposed to either 7,12-dimethylbenz(a)anthracene or γ -ray irradiation. The outgrowths were examined at 4.5, 8, 10, or 16 weeks after transplantation, depending on the experiment, and classified as having normal or dysplastic growth. The data indicated that expression of ductal dysplasia was greater in outgrowths derived from 104 than from 105 cells regardless of the developmental state of the outgrowths. When 24 hr elapsed between carcinogen exposure and cell dissociation, expression of lesions in outgrowths derived from 104 cells required active ductal growth, in that lesions that were present in developing outgrowths remodeled and were no longer detectable when the outgrowths completely filled the fat pad. When second-transplant-generation outgrowths were derived from cells of full (nongrowing) first-generation outgrowths, ductal dysplasias were reexpressed but, once again, only within developing outgrowths. Increasing the time between carcinogen treatment and cell dissociation, i.e., 6 days or longer, resulted in both increased frequencies of ductal dysplasias and substantial numbers of lesions which persisted within full outgrowths. These results suggested that the acquisition of the altered growth potential which resulted in ductal dysplasias and the ability of these lesions to gain some autonomy from growth-regulatory mechanisms were separate events that occurred at different times after carcinogen treatment.