Kaposi sarcoma (KS) is an uncommon angioproliferative malignancy that is associated with human herpesvirus 8. Although there has been recent enthusiasm for evaluating immune checkpoint inhibition as a therapeutic option for viral-associated tumors, the clinical utility in this disease is currently unknown. We report a case of advanced classic KS refractory to multiple lines of chemotherapy that experienced a partial response to anti–PD-1 therapy. Comprehensive molecular profiling was performed on a diagnostic tumor biopsy sample. Molecular profiling data from 8 additional male patients with KS were reviewed and compared with those of the index case. The genomic profile of the index case was notable for higher-than-typical somatic mutational burden, including pathogenic mutation in multiple well-described cancer genes, such as TP53, CDKN2A, NOTCH1, and KRAS. Our case suggests that further clinical study of checkpoint inhibitor therapy in classic KS is warranted, and provides a hypothesis for future immunogenomic biomarker analysis in this disease.