The antitumor effect of IL-9 is also shown in the following aspects: IL-9 can inhibit the growth of human melanoma cells; IL-9 restrains the proliferation and induces the apoptosis of HTB-72 melanoma cells by upregulating the expression of the apoptosis-promoting molecule TRAIL and the antiproliferation molecule p21 [15]; and in most of the solid tumors, IL-9 can directly promote the apoptosis of tumor cells or activate innate and adaptive antitumor immunity. This evidence concerns the gene CDKN1A and melanoma.