The present invention relates to phthalimide carboxylic acid derivatives of formula (I), methods for their preparation, pharmaceutical compositions containing them and their use in medicine, specifically in the treatment of cancer. (I), wherein X is O or S; R.sup.1 is a phthalimide carboxylic acid group of formula (II). R is hydrogen, C.sup.1 C.sup.6 alkyl, aryl or C.sup.1 C.sup.3 alkylaryl and R.sup.2, R.sup.3 and R.sup.4 represent various substituents ##STR00001##