Research appearing in the International Journal of Oncology (2005; 26(3):713-20 (ISSN: 1019-6439)) shows that vitamin K has some anti tumor activity. The tests were performed on human hepatocarcinoma cells (or HCC, cancer cells from the liver). This was not a human study. The effect was tested in vitro (i.e. in a Petrie dish) and in mice who had the cancer cells injected under their skin. It was found that vitamin K2 and K3 had a potent anti tumor effect.