Daniel O'Neil

Daniel O'Neil, MD, MPH is an Assistant Clinical Professor of Medicine specializing in Medical Oncology at Yale School of Medicine. He serves as an Affiliated Faculty member at the Yale Institute for Global Health and a Clinical Member of the Yale Cancer Center. Dr. O'Neil provides clinical care for breast cancer patients at Smilow Cancer Hospital in Waterbury, Connecticut.

Dr. O'Neil's research focuses on two primary areas: understanding the quality of breast cancer care in low- and middle-income countries and investigating the impact of HIV co-infection on breast cancer outcomes. His work has adapted quality metrics from high-resource settings to assess care in Rwanda and South Africa, examining treatment adherence, delays, and standard of care delivery. His research has demonstrated that the higher mortality rates among women with both HIV and breast cancer are not primarily due to differences in cancer care quality.

His publication record shows consistent output in high-impact oncology and global health journals, with a focus on breast cancer in Sub-Saharan Africa. His research spans clinical outcomes, quality assessment, early detection methods, and the intersection of infectious disease and oncology.

Dr. O'Neil has received recognition for his work, including Susan G. Komen grants as noted in Yale Cancer Center news from June 2025. His research has significant implications for improving cancer care in resource-limited settings worldwide.

As a clinician, Dr. O'Neil treats women with breast cancer of all stages and subtypes, emphasizing multidisciplinary care and evidence-based practices. He strongly believes in incorporating a holistic understanding of each patient to provide truly personalized care, drawing on his global health perspective to appreciate diverse patient experiences and needs.

His laboratory and research group, while not formally named in available materials, operates within the Yale Cancer Center's infrastructure, focusing on global oncology research with active collaborations between New Haven and Johannesburg.