Extensive evidence implicates CCR5 and its ligands in the biology of tumors, although there is considerable controversy regarding the role of this chemokine receptor in cancer progression. The discrepancies between the pro- and anti-tumor effects of CCR5 might derive from its expression by cell types with opposing functions in tumor progression and the context in which tumors originate. We propose that CCR5 is necessary for optimal activation of the adaptive immune response to tumors, and for the success of certain immunotherapeutic strategies. Since efficient activation of T cell responses has broad implications in the success of some chemoand radiotherapy protocols, activation of CCR5, rather than its inhibition, might provide new therapeutic opportunities for cancer treatment.