The invention provides NUC-1031 (gemcitabine-[phenyl-benzoxy-L-alaninyl)]-phosphate), a ProTide derivative of gemcitabine, for use in targeting cancer stem cells. This targeting of cancer stem cells may be employed in the prevention or treatment of cancer. The invention also provides NUC-1031 for use in treatment of relapsed or refractory cancer in a human patient. Without wishing to be bound by any hypothesis, it is believed that the ability of NUC-1031 to target cancer stem cells contributes to its utility in the treatment of relapsed or refractory cancers.
