An object of the present invention is to provide a substance which is effective for suppressing or preventing metastasis of cancer, and for suppressing terminal cancer accompanied by metastasis and growth of the metastatic cancer. A composition for suppressing or preventing metastasis of cancer in a subject having cancer, or for suppressing the growth of terminal cancer accompanied by metastasis and / or the growth of metastatic cancer, comprising gaseous hydrogen as an active ingredient. In addition, a method for suppressing or preventing metastasis in a subject, or suppressing the growth of terminally associated cancer with metastasis and / or the growth of the metastatic cancer, comprising administering the composition to a subject having cancer. [Selection diagram] FIG.【課題】癌の転移の抑制又は予防、並びに、転移を伴う末期癌及びその転移癌の増殖の抑制に有効な物質を提供する。【解決手段】気体状水素を有効成分として含む、癌を有する被験体において癌の転移を抑制又は予防する、或いは転移を伴う末期癌及び／又はその転移癌の増殖を抑制するための組成物、並びに、この組成物を、癌を有する被験体に投与することを含む、被験体において転移を抑制又は予防する、或いは、転移を伴う末期癌及び／又はその転移癌の増殖を抑制する方法。【選択図】図５
