The antiproliferative effect of the NGR-Dau conjugates 1 and 2 and free Dau was investigated in vitro on CD13(+) Kaposi’s sarcoma cells (KS) and on CD13(−), but integrin positive [63] HT-29 human colorectal adenocarcinoma cells, as well as on MRC-5 (human fibroblast) as non-cancerous control cell line. This evidence concerns the gene ANPEP and Kaposi's sarcoma.