Tumor specimen will be retrieved from the Departments of Pathology in Lausanne, Geneva and Zurich in the beginning of 2009. The MSI analysis is a straightforward procedure, which takes about 24 hours in the laboratory of Dr Hutter. Thus, the analysis of the 15 specimen in the HIV-positive population will be completed by the end of March 2009. Further decision regarding subsequent analyses in the HIV-negative population will then be subjected to decision, according to the results obtained in these initial tumors.