We have shown for the first time that the pleurocidin-family CAPs NRC-03 and NRC-07 are cytotoxic for multiple breast cancer cell lines, including MCF7-TX400 cells that overexpress P-glycoprotein, and slow-growing SKBR3 cells that contain a 100% ALDEFLUOR-positive breast cancer stem cell population. Here, CAPS is linked to breast cancer.