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 treat - ment of cancer. The invention also provides NUC-103 1 for use in treatment of relapsed or refractorycancer in a human patient. Without wishing to be bound by any hypothesis, it is believed that the ability of NUC-103 1 to target cancer stem cells contributes to its utility in the treatment of relapsed or refractory cancers.
