The ddPCR-based assay for CDKN2A copy number analysis was evaluated by mixing DNA from CDKN2A homozygously deleted U87-MG cells with tumor DNA from a glioma that had retained both CDKN2A copies by ddPCR analysis (copy number: 1.85 ± 0.02). The gene discussed is CDKN2A; the disease is central nervous system cancer.