The initial analysis of 15 HIV-positive patients will be performed free of charge by Pierre Hutter. The cost for molecular study is estimated at 250.-CHF per case. Thus, in case the analysis of MSI in this group leads to promising results, it is estimated that the cost of analysis in 12-15 HIV-negative patients will cost around 3,000.-CHF. Funding for this type of research will be available through the Fonds de Service of Department of Surgery at University Hospital Geneva.