Leo Loeb (1869-1959), was a renowned German-American physician and experimental pathologist. Leo received his M.D. in 1897. For his senior thesis was on skin transplantation in animals. Influenced by his older brother, Jacques, Leo decided to pursue a career in experimental medicine. Loeb became interested in blood coagulation and the growth properties of malignant cells and developed the cell culture technique as applied to both normal and abnormal tissues. In 1903, he began a series of experiments on the influence on cancer growth by reproductive hormones. In 1907, he published a study that showed breast carcinoma in mice could be hereditary. By 1910, Dr. Loeb had acquired a national reputation for his work on cancer. Loeb showed clearly that the growth of certain epithelial malignancies in animals could be modulated by removal of the ovaries. That work predated clinical application of the same concept in human breast cancer by several decades. Loeb retired from doing active research in 1941. He lived to be 90 and died of natural causes.