Dr. Hahn is an internationally recognized authority in the conduct of bladder cancer novel therapeutic clinical trials and translational investigations. He maintains an active clinical practice and sees patients with urothelial cancers of all locations and stages including non-muscle invasive bladder cancer. He is one of the few oncologists in the world leading a clinical trial in non-muscle invasive bladder cancer. In addition, Dr. Hahn continues to care for patients with non-urothelial genitourinary malignancies including prostate, testicular, and other rare tumors. Dr. Hahn's clinical and translational research interests focus on improving outcomes for patients with urothelial cancers through:

The identification and validation of predictive biomarkers relevant to urothelial cancers, and The identification of novel therapeutic and preventative targets for urothelial cancer patients. In addition to his efforts at Johns Hopkins, Dr. Hahn serves as the bladder cancer chairman of the Eastern Cooperative Oncology Group (ECOG), co-chairs the Hoosier Cancer Research Network genitourinary oncology clinical trials working group, participates on the NCI Bladder Cancer Task Force, and serves on the scientific advisory board of the Bladder Cancer Advocacy Network.

He is currently conducting clinical trials to test new therapies for bladder cancer, including those for early stage bladder cancer.