Therefore, our data suggest that xIAP1 and cIAP1 proteins are responsible, at least in part, for the apoptosis-resistant phenotype in metastatic human colon and breast cancers, and LCL85 overcomes metastatic human colon and breast cancer cell resistance to Fas-mediated apoptosis at least partially through inducing proteasomal degradation of xIAP and cIAP1 proteins. Here, XIAP is linked to breast carcinoma.