The present invention relates to a method of predicting or monitoring the sensitivity of a subject having a tumor to a chemotherapy, a method of selecting an appropriate chemotherapeutic treatment of cancer, a method of screening or identifying a compound suitable for improving the treatment of a cancer, and corresponding kits. The method of predicting or monitoring the sensitivity of a subject having a tumor to a chemotherapy typically comprises a step a) of determining, in a biological sample from said subject, the presence, absence or expression level of at least one of a soluble B7H6 (sB7H6 or sB7-H6) and a soluble MIC (sMIC) and, when the expression level is determined, a step b) of comparing said expression level to a reference expression level, thereby assessing or monitoring whether the subject having a tumor is responsive or resistant to the chemotherapy.