It is an object of the present invention to provide a therapeutic agent for cancer comprising an antibody reacting with a cancer-specific membrane antigen wherein the agent is administered by a novel method for decreasing the number of clinical cases for which trastuzumab administration is ineffective. The present invention provides a therapeutic agent for cancer comprising an antibody reacting with a cancer-specific membrane antigen expressed in epithelial cancer cells, said antibody having antibody-dependent cell cytotoxicity, wherein the therapeutic agent for cancer is used for living individual with epithelial cancer which is positive for the cancer-specific membrane antigen and positive for the KLRG1 ligand, and the time of initiation of administration of the therapeutic agent for cancer is during or after the period when KLRG1-positive immunocytes in the peripheral blood of the living individual is selectively reduced ex vivo.本發明之課題在於提供一種含有針對癌特異性膜抗原之抗體的癌治療劑,其特徵在於:藉由可減少曲妥珠單抗(Trastuzumab)之無效例的新穎方法進行投予。根據本發明,可提供一種癌治療劑,其特徵在於:其係含有針對於上皮性癌細胞表現之癌特異性膜抗原的具有抗體依賴性細胞毒殺活性之抗體者,該癌治療劑係用於上述癌特異性膜抗原為陽性、且針對KLRG1之配體為陽性的上皮性癌之生物體,上述癌治療劑之投予開始時期係於上述生物體外選擇性減少上述生物體之末梢血液中之KLRG1陽性免疫細胞的期間或之後。
