Inhibitor of apoptosis levels in breast cancer. Inhibitor of apoptosis (IAP) expression in a panel of normal and breast-cancer-derived cell lines was examined by immunoblotting with antibodies for (a) XIAP, (b) cIAP1 and cIAP2 (blotted sequentially) and (c) Survivin. Survivin and XIAP were detected on the same blot, which was stripped and reprobed for calnexin. (d) IAP expression was also determined in the MCF10 progression panel: (i) cIAP2, XIAP and Survivin and (ii) cIAP1. Representative blots from four experiments for the cell lines are shown. The receptor status of each cell line, determined by western blotting, is shown; there is no correlation with IAP expression. ER, oestrogen receptor; EGFR, epidermal growth factor receptor.