The preset invention relates to a new approach for treating a cancer, particularly a malignant, MDR cancer, a recurrent cancer or a metastatic cancer, using a specific CAP, tilapia piscidin 4 (TP4), which is derived from Nile Tilapia (Oreochromis niloticus). Also provided is a potential therapeutic agent for treatment of triple negative breast cancer (TNBC) which comprises TP4.本發明係關於一種使用特定CAP、從尼羅河吳郭魚(Oreochromis niloticus)衍生的吳郭魚抗菌蛋白4(TP4)治療癌症的新方法,具體而言是惡性、多重抗藥性癌症、復發性癌症或轉移性癌症。還提供了一種用於治療三陰性乳癌(triple negative breast cancer,TNBC)、包含TP4的潛在治療劑。