The purpose of the invention is to provide a method for identifying molecules involved in refractory cancers. Furthermore, the purpose of the invention is to provide a method for identifying drugs effective against refractory cancers. Additionally, the purpose of the invention is to provide a drug effective against recurrent cancers. Provided is a method for screening for molecules involved in refractory cancers, wherein the expression level of an EMT-associated molecule at pre- and post-administration of an anticancer agent is measured in stromal cells and/or cancer cells in tissue that reconstructs the cancer microenvironment, and an EMT-associated molecule presenting a higher expression level at post-administration of the anticancer agent than at pre-administration is scored as being involved in refractory cancers. Also provided is a method for screening for drugs effective against refractory cancers, wherein the expression level of an EMT-associated molecule at pre- and post-administration of an anticancer agent is measured in stromal cells and/or cancer cells in tissue that reconstructs the cancer microenvironment, and an EMT-associated molecule presenting a higher expression level at post-administration of the anticancer agent than at pre-administration is scored as being involved in refractory cancers, while a substance that can inhibit the function of this EMT-associated molecule is scored as a drug effective against refractory cancers. Further provided is a drug for treating and/or preventing tumor recurrence as a combination of an anticancer agent with an inhibitor targeted to the NOTCH3 signal.L'objectif de la présente invention est de fournir un procédé d'identification de molécules impliquées dans des cancers réfractaires. En outre, l'objet de l'invention est de fournir un procédé d'identification de médicaments efficaces contre des cancers réfractaires. De plus, l'objectif de l'invention est de fournir un médicament efficace contre des cancers récurren
