Dr. Cairncross is best known for contributions to neuro-oncology. He discovered that oligodendroglioma, a type of brain cancer, is sensitive to chemotherapy, and he and David Louis co-discovered a molecular marker of their drug sensitivity. Testing for this marker is now used worldwide to guide the treatment of patients with oligodendroglioma. A trial led by Dr. Cairncross showed that patients with this genetic subtype of oligodendroglioma live twice as long when chemotherapy is a part of their treatment. His contributions to the understanding and treatment of brain cancer have been cited nearly 50,000 times.