An anti-CTLA4 antibody or an antigen-binding portion thereof for use in the treatment of mesothelioma, wherein the anti-CTLA4 antibody or antigen-binding portion thereof is to be administered to a patient suffering from mesothelioma as monotherapy in a multiple dose regimen, each dose having a dosage in the range of 1-20 mg/kg body weight, wherein the heavy chain CDR1-3 and light chain CDR1-3 of said antibody comprise the amino acid sequences set forth in a) SEQ ID NOs: 1-6, respectively； b) SEQ ID NOs: 9-14, respectively； c) SEQ ID NOs: 17-22, respectively； or d) SEQ ID NOs: 25-30, respectively.
