Disclosed herein is a method for enhancing sensitivity of cancer cells to compounds or radiation by inhibiting the expression of testis-specific protein, Y-encoded like 5 (TSPYL5). More specifically, because methylation of TSPYL5 protein expressed in lung cancer cell line was inhibited to increase the expression level of the gene, resistance to stress such as radiation or anticancer agents was increased. Because the sensitivity of cancer cells to stress such as radiation or anticancer agents was increased by inhibiting the expression of the TSPYL5 gene to promote the apoptosis of the cells, an anticancer supplement agent containing an inhibitor of the expression or activity of the TSPYL5 gene of the present invention inhibits the growth of cancer cells and enhances the sensitivity to various stresses to maximize the apoptosis. Thus, when used in combination with radiotherapy or chemotherapy, the anticancer supplement agent may be used very usefully for anticancer treatment.