Clusterin (apolipoprotein J) is a 75 - 80 kDa disulfide-linked heterodimeric protein associated with the clearance of cellular debris and apoptosis. It is a stress-induced cytoprotective chaperone protein regulated by HSF1 and functions similarly to a small heat- shock protein. Clusterin is distributed widely in human tissues and fluids, including normal epithelial cells, plasma, cerebrospinal fluid, breast milk, semen and urine. Clusterin is expressed in a wide variety of hematopoietic and non-hematopoietic tumors. It is present in 80– 100% of systemic anaplastic large cell lymphomas. Adding clusterin to antibody panels designed to distinguish systemic anaplastic large cell lymphoma from classical Hodgkin's disease is useful. In a study by Grogg et al. on 202 spindle cell tumors, Clusterin was found to be highly sensitive and specific for follicular dendritic cell tumors. Overexpression of Clusterin is associated with poor prognosis and recurrence in breast cancer. Expression of Clusterin in cervical cancer is correlated with chemosensitivity and predicts poor survival.