Immunohistochemistry is indispensable in resolving these diagnostic dilemmas: markers such as PD-1, Bcl-6, and CD10 highlight the TFH nature of AITL [4,5,32], whereas HHV-8 LANA-1, ERG, CD31, and CD34 confirm KS [12]. The gene discussed is PECAM1; the disease is Kaposi's sarcoma.