Hydroxyurea has been used for decades and it is still valuable for the treatment of some types of cancer. It inhibits ribonucleotide reductase (RNR) enzyme known to be crucial in the conversion of ribonucleotides into deoxyribonucleotides. However, nowadays the main focus has shifted to structurally similar hydroxamic acid derivatives that target specific enzymes involved in cancer progression such as histone deacetylases, matrix metalloproteinases and also RNR.