MSI reflects genomewide instability (resulting from a deficient MMR system), and occurs at increased frequency in HIV-associated cervical intraepithelial and lung neoplasia. In both cases, the frequency of MSI was six fold greater in the HIV-associated tumors, compared with tumors of HIV-indeterminate patients [7]. Others authors have also reported a high rate of MSI in Kaposi's sarcomas and aggressive lymphomas obtained from HIV-infected patients, whereas there is no evidence of similar instability in lesions from HIV-negative patients [8]. The recent observation that the MSI phenotype is restricted to HIV-related lymphomas suggests that a cardinal feature of cancer, such as genetic instability, can be highly influenced by host immunity [9].