Abstract: The present disclosure provides a system for discovering a novel target protein and a companion diagnostic biomarker therefor, the system comprising: a patient group classification unit specifying a single gene and dividing a high-expression patient group and a low-expression patient group according to an expression level of the single gene; a prognostic association calculation unit calculating prognostic association values of all genes in the high-expression patient group and the low-expression patient group; a prognostic association comparison unit comparing prognostic association values of the high-expression patient group and prognostic association values of the low-expression patient group for all genes; and a biomarker selection unit selecting a biomarker to divide a patient group from the comparison value.