The present invention provides an anti-cancer agent which comprises a human antibody light chain having a cytotoxic activity against cancer cells, especially against lung cancer cells, as an active ingredient. The anti-cancer agents of the present invention mainly comprise a polypeptide having an amino acid sequence of SEQ ID No. 1, 9 or 13, a polypeptide in which one or several amino acids are substituted, added or deleted, wherein the polypeptide forms dimer and the polypeptide is a human antibody kappa light chain, or a polypeptide having an amino acid sequence of SEQ ID No. 19, a polypeptide in which one or several amino acids are substituted, added or deleted, wherein the polypeptide forms monomer and the polypeptide is a human antibody kappa light chain.本發明提供一種以對於癌細胞(特別是肺癌細胞)表現出細胞毒性之人類抗體輕鏈作為有效成份之抗癌劑。本發明之抗癌劑主要的特徵在於包含下述人類抗體κ型輕鏈：由多肽構成且為二聚體之人類抗體κ型輕鏈，該多肽之可變區係以序列編號1、9或13之胺基酸序列，或者該等胺基酸序列中有1或數個胺基酸經取代、附加或缺失之胺基酸序列來表示；或者，由多肽構成且為單體之人類抗體κ型輕鏈，該多肽之可變區係以序列編號19之胺基酸序列，或者該等胺基酸序列中有1或數個胺基酸經取代、附加或缺失之胺基酸序列來表示。
