Factors influencing differential growth of rat mammary tumor fragments and cells transplanted in gland-free and gland-containing mammary fat pads.

Transplants from eight primary tumors induced by 7,12-dimethylbenz(a)anthracene were placed into gland-free and gland-containing inguinal mammary fat pads of syngeneic female hosts. Samples were transplanted as 1 mm3 fragments or as cell suspensions of enzymatically dissociated tumors averaging 1.5 X 10(5) cells/ml. Similar differential growth patterns resulted from both types of transplants. In samples from two of eight tumors fragments produced more tumors than did dissociated transplants, regardless of fat pad condition. In one case dissociated transplants gave rise to more tumors than did fragments. Samples from two of eight tumors produced no differences in tumor growth from fragments and dissociated transplants. Samples from the remaining two showed low transplantability. Overall, no significant differences in tumor growth could be attributed to transplant treatment or fat pad condition. Gland-containing fat pads inhibited ductal outgrowth following transplantation while gland-free fat pads favored it. From the data, the greater the lability of the primary tumor, the greater the influence of the host microenvironment on the outgrowth potential of the tumor.