Clusterin is a multifunctional glycoprotein whose role in cells has generated a great controversy in recent years. Since its discovery, numerous studies have linked clusterin expression deregulation with various physio-pathological processes such as cancer or Alzheimer's disease. Although the results of such investigations have sometimes been contradictory, mainly due to the dichotomous role of clusterin isoforms, it has been demonstrated that this protein is involved in diverse cellular processes, including apoptosis, cell cycle regulation, DNA repair or the acquisition of cell resistance against multiple conventional therapies. These results, together with the breakthrough of gene therapies, have motivated a great effort to elucidate the importance of clusterin as a potential therapeutic target. However, the understanding of a single gene, with multiple RNA transcripts and several protein isoforms has turned out to be a complex task. In this review, we summarize the studies published to date on factors that can affect clusterin expression and evaluate if a better understanding of this complex gene/protein would be useful to develop new treatment strategies for cancer and other pathologies.