I have been a proponent of Vitamin C as supportive treatment of cancer for many years. I utilize intravenous vitamin C in higher doses than normal. There were only two studies that do not support this and the patient population were less than 50 patients. I have seen vitamin C in higher doses have many beneficial properties.
There are high molecular weight substances as mushrooms extracts like PSK and even ligans from pine cones that can increase vitamin C oxidation and synergistically enhance the cytotoxic effects of vitamin C. This has been shown and studied in human leukemia and brain caner cells.
There also is a synergistic effect seen with Vitamin K. Vitamin K3 potentiates the cytotoxic effects of Vitamin C in vitro and requires a 1:100 ratio. This is not always possible. It can be done in intravenous form, but this is not always possible for many practitioners.