Disclosed are compositions and methods for modulating cancer stem cells. More particularly, the present invention discloses the use of lysine demethylase (LSD) inhibitors and protein kinase C theta inhibitors (PKC-θ) for inhibiting the growth of LSD- and/or PKC-θ-overexpressing cells including cancer stem cells, for enhancing the biological effects of chemotherapeutic drugs or irradiation on cancer cells, for treating cancer, including non-metastatic and metastatic cancer and/or for preventing cancer recurrence.