The present invention provides a method for predicting the therapeutic effect of chemotherapy using an anti-tumor agent that contains trifluridine and tipiracil hydrochloride at a molar ratio of 1:0.5 on a colorectal cancer patient, said method comprising the steps (1)-(3) that are indicated below. As a means of solving the problem addressed by the present invention, a method comprising the following steps is provided: a step (1) in which the expression of the TK1 protein in the cytoplasm of a tumor cell that is included in a biological sample taken from the patient is detected using immunohistochemistry a step (2) in which tumor cells are classified as positive cells and negative cells from the detection result obtained at step (1) and the share of positive cells among the tumor cells is calculated and a step (3) in which, when the share is 30% or higher, it is predicted from the calculation result obtained at step (2) that there is a high possibility that chemotherapy using an anti-tumor agent that contains trifluridine and tipiracil hydrochloride at a molar ratio of 1:0.5 will have a sufficient therapeutic effect on the patient.La présente invention concerne une méthode de prédiction de leffet thérapeutique dune chimiothérapie au moyen dun agent anti-tumoral qui contient de la trifluridine et du chlorhydrate de tipiracil dans un rapport molaire de 1:0,5 chez un patient atteint dun cancer colorectal, ledit procédé comportant les étapes (1) à (3) qui sont indiquées ci-dessous. Une solution au problème abordé par linvention porte sur un procédé comportant les étapes suivantes : (1) lexpression de la protéine TK1 dans le cytoplasme dune cellule tumorale comprise dans un échantillon biologique prélevé chez le patient est détectée à laide dune immunohistochimie (2) les cellules tumorales sont classées en cellules positives et en cellules négatives selon le résultat de la détection obtenu à létape (1) et la part des cellules positives parmi les cellules tumorales est c
