Disclosed is a method for determining the efficacy of GPC3-targeted therapeutic agent therapy for a patient or against a cancer in the patient, prior to receiving GPC3-targeted therapeutic agent therapy, or for determining whether to continue GPC3-targeted therapeutic agent therapy for a patient, wherein the method includes a step of monitoring the free GPC3 concentration in a biological specimen isolated from a patient prior to receiving GPC3-targeted therapeutic agent therapy and/or a patient having received GPC3-targeted therapeutic agent therapy, and determining the GPC3-targeted therapeutic agent therapy to be effective, or determining to continue the GPC3-targeted therapeutic agent therapy, when the free GPC3 concentration is a predetermined value. Also disclosed is a GPC3-targeted therapeutic agent or drug formulation for further administration to a patent for whom GPC3-targeted therapeutic agent therapy has been determined effective, or for whom it has been determined to continue GPC3-targeted therapeutic agent therapy.
