To provide a method and a diagnostic kit for determining the presence of a malignant tumor or the severity thereof, a method for selecting a therapeutic method therefor or evaluating the effect of the therapeutic method, or a method for estimating the risk of recurrence of the malignant tumor or determining the presence or absence of the recurrence. The method for determining the presence of a malignant tumor or the severity thereof, method for selecting a therapeutic method therefor or evaluating the effect of the therapeutic method, or method for estimating the risk of recurrence of the malignant tumor or the presence or absence of the recurrence is characterized by including 1) a step of measuring the concentration and/or quantity of soluble LR11 in a sample originating from a subject and 2) a step of comparing the value measured above with a measurement value of soluble LR11 obtained from a healthy subject group.
