The present invention is related to a method for treating cancer metastasis and composition thereof. By using an IL-35 antagonist, cancer metastasis can be effectively treated so that an increased cancer free and overall survival can be achieved.本發明涉及治療癌症轉移之方法及其組合物。透過使用IL-35拮抗劑,可以有效地治療癌症轉移,從而可以達到增加的癌症痊癒及整體存活期。