CDK4/6 Inhibition With Anti-PD-1 Checkpoint Blockade Induces Major Response in Aggressive Classic Kaposi Sarcoma After Previous Progression on Anti-PD-1 Alone Representative pathology slides from the left lower extremity amputation specimen demonstrate small residual nodules of Kaposi sarcoma with (A) human herpesvirus-8 positivity, (B) a lymphocytic infiltrate, and (C) CDK4 expression (a CDK6 immunostain was not available for clinical use). KS is encountered in four epidemiological settings reflective of immunosuppression and HHV-8 seroprevelance patterns: classic (initially described in 1872 and affecting Mediterranean populations), endemic (occurring in sub-Saharan Africa), HIV/AIDS-related, and iatrogenic (solid-organ transplant recipients).[1] An improved understanding of KS and HHV-8 pathobiology has enabled new therapeutic approaches for this disease. Kaposi sarcoma (KS) is a virally driven malignancy associated with human herpesvirus-8 (HHV-8) infection of endothelial cells. [Extracted from the article]