The present invention relates to synergistic combinations of the compounds of formula I such as compounds of the xanthenone acetic acid class such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and NSAIDs, in particular diclofenac, which have anti-tumor activity. More particularly, the invention is concerned with the use of such combinations in the treatment of cancer and pharmaceutical compositions containing said combinations.