The objective of this study is to determine what role prolactin plays in the maintenance and treatment of human breast and prostate cancer. A multifaceted approach is envisioned including in vitro and in vivo observations. The effects of prolactin on normal and cancerous breast tissue will be evaluated by growing tissues in organ culture with various combinations of hormones. Histological, histochemical and radiochemical methods will be used to examine the results. It is hoped these studies may provide a means to analyze the growth characteristics of tissues from individual cancer patients and predict logical treatment courses. In order to observe and correlate the dynamics of circulating prolactin with progression or remission of breast cancer we will launch a comprehensive clinical program. We will test the ability to stimulate and suppress prolactin in breast cancer patients. Prolactin will also be studied before, during, and after various treatments including drugs and surgery. The response of the prolactin in these instances will be correlated with the patient's clinical course. Similar culture methods will be used to determine if prolactin has an effect on normal or diseased human prostate tissue. Tissues obtained at surgery will be grown in organ culture. The effect of prolactin and in combination with other hormones will be evaluated by examining the histological, histochemical and radiochemical effects. A clinical program to examine prolactin in patients with cancer of the prostate will be undertaken and the effect of orchiectomy, prostatectomy, hypophysectomy, treatment with estrogens, progestational agents and antimetabolites on prolactin will be tested.