PROBLEM TO BE SOLVED: To provide a new medicinal application of a water-soluble component originated from feather.SOLUTION: The new medicinal application is a proliferation inhibitor of a tumor cell, containing the water-soluble component obtained by subjecting the feather to solubilizing treatment, or the water-soluble component obtained by subjecting the feather to the solubilizing treatment and further treating the treated product with a proteolytic enzyme, as an active ingredient. As a result, there is provided a new utilization method of the feather of poultry farming which has been discarded, for example, by being burned or being filled in a land.【課題】 羽毛由来の水溶性成分の新規な医薬用途を提供すること。【解決手段】 羽毛を可溶化処理して得られる水溶性成分、または、羽毛を可溶化処理した後、タンパク質分解酵素で処理して得られる水溶性成分を有効成分とする腫瘍細胞増殖抑制剤である。本発明によれば、例えば焼却したり埋め立てたりして処分されている養鶏の羽毛の新たな利用方法が提供される。【選択図】 図３
