Holland is currently the Emily Tow Jackson Chair in Oncology and the founding director of the Brain Tumor Center at Sloan-Kettering, where he has built one of the nation's most successful brain cancer research and clinical programs. He specializes in the research and treatment of glioma – the most common brain cancer in adults – and metastatic brain tumors.Throughout his career Holland has worked at the intersection of multiple disciplines to address the molecular basis of brain tumors and develop new approaches to their treatment. His research focuses on developing mouse models of brain cancer that mimic the behavior of the disease in patients. His work with mouse models has led to clinical trials in glioma patients. He also has developed imaging strategies to follow mouse brain tumors as they develop – a powerful system that is used to test promising new drugs with potential benefit for patients. Among Holland's discoveries:
- He was the first to use a system of postnatal gene transfer to study brain cancer formation in mice, providing a model for the development of gliomas and medulloblastomas.
- His laboratory was the first to demonstrate that stem cells are more sensitive to changes that can lead to cancer, providing clues to cancer development and its ability to evade treatment.
- He was the first to demonstrate that the activity of a protein called Akt is elevated in human glioblastomas – a finding that provided major insights into the development of this cancer.