In agreement with our previous report [19], indicating that apoptosis induction was less likely to contribute to the cytotoxicity in U-87 cells caused by arenobufagin, neither apoptotic cells (annexin V-positive cells) nor the activation of caspases was observed in the cells treated with arenobufagin alone (Figure 5 and Figure 6), although arenobufagin has been demonstrated to induce breast cancer MCF-7 cells and cervical carcinoma HeLa cells to undergo apoptosis [43,47], suggesting that induction of apoptosis by arenobufagin may be cell-specific. Here, ANXA5 is linked to breast carcinoma.