Organ Cultures of Mouse Mammary Tumors In Various Hormonal Environments: An Ultrastructural Study 1. 2

SUMMARY-To obtain an in vitro system capable of producing the BiHner virus in quantity and amenable to an ultrastructural study, mammary tumors of mice (PS strain) were grown in organ cultures with the use of a technique of culture on stainless-steel grids mounted in specially devised petri dishes. Mammotropin, somatotropin, and estrogen were added in various combinations and at various doses to a basic medium that always contained insulin. After 5 and 9 days of culture, the tumor Fragments were prepared For ultrastructural examination. The ultrastructure of the tumors at the end of cultivation was well preserved and a certain degree of differentia-tion could occur in vitro. This ultrastructure was hardly modified in the presence of the various hormones used. Finally and most important, virus production was abundant. All stages of Formation of virus by budding at the surface membrane consistently occurred in all cases.-J Nat Cancer Inst 42: 545-558 " 1969. FEW ORGAN cultures of mouse mammary tumo