Disclosed is a use of the CUEDC2 protein in the preparation of diagnostic agents for prognostic determination of the endocrine drug therapy for the breast cancer patients and diagnosis of tumors such as breast cancer and ovarian cancer. The diagnostic agent comprises an antibody against the CUEDC2 protein, wherein the antibody is a monoclonal or polyclonal antibody against the CUEDC2 protein. Provided is a kit or a composition for prognostic determination of endocrine drug therapy for the breast cancer patients and diagnosis of tumors such as breast cancer and ovarian cancer. The kit or composition comprises an antibody against the CUEDC2 protein. Further disclosed is a use of the CUEDC2 gene or protein in preparation of drugs for treating tumors, that is, small molecular substances and specific antibodies that specifically inhibit the expression or activity of the CUEDC2 gene\protein are used as a therapeutic agent to restore the sensitivity of drug-resistant tumors to drug treatment. The new use of the CUEDC2 protein provides a new basis for determining a dosage regimen of adjuvant therapy after surgical operation of the breast cancer patients, thereby improving the therapeutic effect of the anti-cancer drugs and alleviating the suffering and economic burden of the patients.Linvention concerne lutilisation de la protéine CUEDC2 dans la préparation dagents diagnostiques pour la détermination pronostique du traitement médicamenteux endocrinien pour les patients atteints dun cancer du sein et le diagnostic de tumeurs telles que le cancer du sein et le cancer ovarien. Lagent diagnostique comprend un anticorps contre la protéine CUEDC2, lanticorps étant un anticorps monoclonal ou polyclonal contre la protéine CUEDC2. Linvention concerne un kit ou une composition pour la détermination pronostique du traitement médicamenteux endocrinien pour les patients atteints dun cancer du sein et le diagnostic de tumeurs telles que le cancer du sein et le cancer ovarien. Le kit ou l
