Exome sequencing reveals a sparse genomic landscape in Kaposi sarcoma.

Kaposi Sarcoma (KS) is a frequently aggressive malignancy caused by Kaposi sarcoma herpesvirus (KSHV/HHV-8). People with immunodeficiencies, including HIV, are at increased risk for developing KS, but our understanding of the contributions of the cellular genome to KS pathogenesis remains limited. To determine if there are cellular genetic alterations in KS that might provide biological or therapeutic insights, we performed whole exome sequencing on 78 KS tumors and matched normal control skin from 59 adults with KS (46 with HIV-associated KS and 13 with HIV-negative KS) receiving treatment at the Uganda Cancer Institute in Kampala, Uganda. We found a very low mutational burden in all but one specimen (median=11 mutations), which is the lowest number of mutations among all 33 tumor types in The Cancer Genome Atlas (TCGA). No recurrent mutations were seen and the most commonly affected oncogenic pathway was RTK/RAS. Mutational signatures included defective DNA mismatch repair and smoking. There was no evidence suggesting that multiple tumors from the same patient originated from the same original clone. The number of genome copy alterations per genome were higher in tumors from those without HIV infection and in tumors from participants with advanced stage disease, suggesting that lesions that take longer to develop may accumulate more alterations, although the number of alterations remain low compared to other cancers. Implications: Our findings indicate that the pathogenesis of KS differs from other malignancies, and that the primary driver of carcinogenesis is KSHV viral infection and expression of viral oncogenes, rather than clonal oncogenic transformation.