In order to gain an understanding of the nature of hormonal dependency and autonomy of breast cancers, a basic understanding of the action of hormones at the cellular and subcellulr level will be required. Two experimental mammary tumors in rodents are being studied. To examine the actions of insulin at the cellular level, we will employ dissociated tumor cells from hormonally modified animals, and will examine in vitro the characteristics of insulin binding to its receptor, the actions of insulin on glucose and amino acid transport, the utilization of the transported substrates and the effects of estrogen and other hormones on the regulation of insulin binding and its action in these tumors. Short-term tissue culture of tumor cells, which has been initiated successfully, will be used to examine hormonal regulaton of insulin and estrogen binding in vitro, and the effects of these hormones on growth and metabolism of these cells. Since we perceive that insulin has both direct and permissive actions, the ultimate goal of the studies is to define these actions of insulin and determine how these may be modified by other hormones, and to relate such mechanisms to tumor growth and its control.