Preferential growth of mammary tumors in intact mammary fatpads

Four transplantable tumors, three (66, 410, and 168cl) isolated from a spontaneously occurring strain BALB/cfC3H mammary tumor and one (D2) arising from a BALB/c hyperplastic alveolar nodule were found to grow better in mammary fatpads than at s.c. sites. Furthermore, tumor growth was better (p less than 0.05) in intact mammary glands than in cleared mammary fatpads for the D2, 410, and 66 tumors (168cl was not tested). The role of immunity in these differences was investigated using the highly immunogenic 410 tumors. Tumor 410 induced equally effective immunity to subsequent challenge whether it was implanted s.c. or in intact fatpads. Furthermore, in immunized animals, Tumor 410 was rejected equally well when the challenge site was intact fatpad as when s.c. Similarly, Tumor 410 induced immunity after implantation into cleared fatpads and, in immunized animals, was rejected when the challenge site was the cleared fatpad. We thus found no evidence that the mammary fatpad is immunologically privileged, as compared to the s.c. site, with respect to tumor transplantation antigens.