Embryonic inductive tissues that cause histologic differentiation of murine mammary carcinoma in vitro

A murine mammary tumor was cultured in vitro for 14 days, either in direct combination with various embryonic murine inductive tissues or separated by a Millipore filter from these tissues. From 456 test cultures and 269 control cultures of tumor alone, morphologic, histochemical, and autoradiographic evidence for cytodifferentiation was obtained in the tumor after exposure to inductive tissues directly or through the filter. There appeared to be a gradient in potency of the inductive tissues; embryonic mammary mesenchyme was the most active of the tissues tested. Tumor growth was not different from that of controls, however, when the cultured, inductive tissue-exposed neoplasm was returned to the murine host.