It is an object of the present invention to provide a novel method for decreasing the number of clinical cases for which trastuzumab administration is ineffective. The present invention provides a method for treating a living individual with epithelial cancer comprising: step (a) of selectively reducing KLRG1-positive immunocytes in the peripheral blood of a living individual with epithelial cancer ex vivo, which is positive for a cancer-specific membrane antigen expressed in epithelial cancer cells and positive for a KLRG1 ligand and step (b) of administering, to the living individual, a therapeutic agent for cancer comprising an antibody reacting with the cancer-specific membrane antigen expressed in epithelial cancer cells and having antibody-dependent cell cytotoxicity.
