In vitro studies have shown that IL-9 could upregulate the P21CIP1 gene in tumor cells to directly induce the proliferation and inhibit the apoptosis of LY1 and LY8 cells in DLBCL, promote the survival of DLBCL cells, and reduce the sensitivity of tumor cells to chemical substances (50). The gene discussed is CDKN1A; the disease is diffuse large B-cell lymphoma.