RB1 and Kaposi's sarcoma: Thus, vascular tumors mimicking Kaposi sarcoma can be categorized into three clusters: cluster 1, altered expression of tumor suppressor genes (p53, p27) with a high proliferative index, enriched AS; cluster 2: high CD44 expression with a low proliferative index suggesting stem cell differentiation, mixed diagnosis; and cluster 3: lymphatic differentiation with activated Rb pathway, enriched KS.