Cathepsin D overexpression can significantly increase G2E3 expression, and blocking G2E3 expression can significantly inhibit hepsin degradation induced by cathepsin D. Immunohistochemical analysis also found G2E3 expression was significantly negatively related to the expression of hepsin and positively related to cathepsin D expression in breast cancer. The gene discussed is CTSD; the disease is breast carcinoma.