As an oncologist, Horn focused her clinical practice on patients with lung cancer, pleural mesothelioma and thymic cancer. She was the principal investigator on several ongoing clinical trials that target those cancers.
Horn was also an associate professor of medicine at Vanderbilt University and the former assistant director of the Educator Development Program, designed to enhance the knowledge, skills and attitudes of Medical Center faculty.
While focusing on experimental therapeutics, she received a Vanderbilt-Ingram Impact Award for her work. The National Cancer Institute further awarded her with a Cancer Clinical Investigator Team Leadership Award in 2015.
Horn received her medical degree from the University of Toronto, where she also did a fellowship in Internal Medicine that was funded by the Canadian Association of Medical Oncology. She did a second fellowship at Vanderbilt-Ingram.
Horn has published more than 30 book chapters and papers, most on her research into lung cancer.
She is a member of the Royal College of Physicians and Surgeons of Canada and the American Society of Clinical Oncology. She is board certified in Internal Medicine.