To further delineate the relationship between tumor purity and somatic mutations, we stratified purity estimates by the mutation status of a panel of recurrently altered genes in prostate cancer.8 Tumor purity determined by at least one profile was associated with six genes, including ERG fusions and SPOP, FOXA1, and TP53 point mutations (false discovery rate [FDR]–adjusted P < .25, Wilcoxon rank sum test; Fig 3D, Data Supplement Table 3). The gene discussed is ERG; the disease is prostate cancer.