Recent concepts in the evaluation of non cytotoxic anti-cancer drugs such as anti-angiogenic agents suggest novel criteria for the design of clinical studies due to the specific mechanism of action of these drugs. In particular, the use of the conventional evaluation criteria based on cytotoxic actions may mislead the interpretation of the therapeutic efficacy of non cytotoxic agents. The study was therefore designed to compare the clinical response to Indinavir in early-stage vs. late-stage KS and by relating it to key biological endpoints and plasmatic drug concentrations. This was also motivated by the rareness of C-KS and by ethical reasons which prevented the inclusion of a control group.