Daniel O'Neil, MD, MPH

Daniel O’Neil, MD, MPH, is an Assistant Clinical Professor of Medicine (Medical Oncology) and cares for patients with breast cancer as part of the Smilow Cancer Hospital Care Center in Waterbury. 

Dr. O’Neil received his medical degree from Albert Einstein College of Medicine and completed his residency at Brigham and Women's Hospital in both Internal Medicine and Global Health Equity, and fellowship at NewYork-Presbyterian/Columbia University Medical Center. He received his MPH with a focus on epidemiology at Harvard T.H. Chan School of Public Health. 

Dr. O’Neil is also a global oncology breast cancer researcher. He is particularly interested in understanding the quality of breast cancer care delivered in low- and middle-income countries.

Dr. O’Neil treats women with breast cancer of all stages and subtypes, as well as women with high-risk benign breast lesions. He strongly believes in the value of multidisciplinary patient care and collaboration. He aims to incorporate the latest evidence-based practices, alongside a holistic understanding of each of his patients, to offer truly personalized care.

He studies the impact of comorbid HIV on breast cancer outcomes. Women living with both HIV and breast cancer consistently demonstrate higher overall mortality than women living with only breast cancer. Dr. O'Neil's comparisons of breast cancer treatment quality in South African women with and without comorbid HIV have shown that this disparity in mortality is not primarily driven by differences in cancer care. He is currently working with collaborators in Johannesburg and New Haven, looking for differences in tumor behavior or anti-tumor immune response in women living with HIV.