Extensive research has indicated that high glucose levels play an important role in cancer. A high glycaemic index, glycaemic load diet, high sugar intake, high blood glucose and diabetes mellitus all increase the risk of cancer. Various signals are involved in high glucose–induced tumorigenesis, cancer proliferation, apoptosis, invasion and multidrug resistance. Reactive oxygen species might be important targets in cancer progression that are induced by high glucose levels. Drugs such as metformin and resveratrol may inhibit high glucose–induced cancer. As the impact of high glucose levels on cancer progression and therapy is a novel finding, further research is required. Keywords: cancer, high glucose, progression, therapy, tumorigenesis