The present invention provides a 1,2,4-trioxane or a pharmaceutically acceptable salt, ester, solvate, tautomer or stereoisomer thereof for use as an adjuvant for a tyrosine kinase inhibitor to enhance the activity of said tyrosine kinase inhibitor in a method for the treatment of a patient suffering from cancer, a pharmaceutical composition comprising a tyrosine kinase inhibitor as an active ingredient and said 1,2,4-trioxane adjuvant or a pharmaceutically acceptable salt, ester, solvate, tautomer or stereoisomer thereof in an amount sufficient to enhance the activity of the tyrosine kinase inhibitor, preferably for use in a method for the treatment of cancer.