Described herein are methods for preventing a relapse of cancer in a subject. The methods involve administering to the subject in need thereof a sulfated glycosaminoglycan or the pharmaceutically acceptable salt or ester thereof. In one aspect, the methods described herein prevent the growth or self-renewal of cancer stem cells in a subject. In another aspect, the methods described herein kill active or dormant cancer stem cells in a subject. The methods described herein can be used in combination with chemotherapy and/or radiation. The methods described herein are versatile with respect to preventing the relapse of a number of different cancers.