In both patient care and research, he focuses on prostate cancer, immunotherapy and how body mechanisms may create resistance to standard therapies.

Small is a member of several professional medical societies, including the American Society of Clinical Oncology and American Urological Association. He is a member of the therapy consortium of CaP CURE, the largest privately funded project to advance prostate cancer research. He is also on the American Prostate Cancer Foundation's board of directors. He chairs the prostate cancer correlative sciences working group for Cancer and Leukemia Group B, a cooperative organization of cancer researchers.