CST6 and breast carcinoma: In addition, epigenetic silencing of the lysosomal cysteine protease inhibitor cystatin 6 (CST6) is more frequently observed in metastatic lesions than in primary cancers [35] and the epigenetic silencing of the chemokine CXCL12 (rather than its receptor CXCR4) contributes to the metastatic potential of mammary carcinoma cells [36].