I have been promoting vitamin K for heart disease and osteoporosis, but I recently became aware that it is also useful for the treatment of many cancers. Most of the research has focused on synthetic vitamin K3 at high doses. It is commonly being used with chemotherapy agents for enhanced effectiveness.
I personally would not advise using the synthetic vitamin K3, but rather the plant-based vitamin K1 (phylloquinone) and bacterially produced vitamin K2 (menaquinone). This study used vitamin K2 to treat lung cancer, but previous studies have shown benefit in leukemias. Typically, large doses of vitamin K are needed and most of the available supplements come in microgram doses. We have a much more concentrated form of vitamin K on the site.
International Journal Oncology September 2003;23(3):627-32