Dr. Hellman has been active in both clinical and laboratory investigation. He has been involved in studies of breast cancer, prostate cancer and lymphoma. The breast cancer studies are of conservative management and the natural history of regionally treated disease. Both of these studies emphasize the importance of understanding the clinical evolution of the disease in order to develop effective multidisciplinary therapy. His laboratory investigations centered on the cell kinetics of the hematopoietic stem and progenitor cells. Dr. Hellman has written on the possible interference with the doctor-patient relationship by clinical research and managed care. He is the author or co-author of over 300 scientific articles in his field and co-editor of the standard textbook on cancer, Cancer: Principles and Practice of Oncology through the 7th edition.