Serum diagnosis for examining the tumor marker in the serum, as well as tissue diagnosis and cell diagnosis by biopsy are conventionally known for cancer diagnosis. However, the reliability thereof is low, or the determination by individuals or determination by medical facilities varies. Thus, a molecular diagnosis based on genes and protein expressed in the living body is recently being reviewed as a standardized diagnosis method for cancer in which variation among diagnostician is small. Various methods such as a method of using cyclin-dependent kinase (hereinafter also simply referred to as “CDK”) have been proposed as a molecular diagnosis based on protein (see e.g., International Publication WO 2005/116241 and International Publication WO 2003/078662).
International Publication WO 2005/116241 discloses a method of measuring a ratio obtained from an activity value and an expression level of the CDK1 (CDK1 specific activity) and a ratio obtained from an activity value and an expression level of the CDK2 (CDK2 specific activity), comparing CDK2 specific activity/CDK1 specific activity with a threshold value set in advance, and determining the malignancy of cancer based on such result. International Publication WO 2003/078662 discloses a method of normalizing the expression level of a predetermined gene such as p52BP2 gene, cathepsin B gene, cathepsin L gene, Ki67/MiB1 gene, thymidine kinase gene, and p27 gene, and an expression product thereof with respect to a control gene, and predicting the clinical result of the patient to compare with the amount derived in a reference cancer tissue set.
In the above methods, the predetermined threshold value set in advance and the measurement value of the parameter are compared, and the state of cancer is predicted and the clinical result is predicted based on the comparison result. However, in such methods, determination is made with the threshold value as the reference even if the measurement value of the parameter is very close to the threshold value. Thus, for example, even with a clinical sample that actually has a high recurrence risk, the determination result different from the actual result is sometimes obtained since the measurement value of the parameter obtained from the clinical sample is slightly lower than or greater than the threshold value. In this case, an accurate determination is not said to be made with the above method, and an accurate diagnosis may not be made if such determination result is used in diagnosis of cancer.