Given that histone deacetylases (HDACs) play crucial roles in regulating gene expression and aberrant HDAC expression is frequently documented in melanomas, it has been demonstrated that HDACs can modulate the transcription of PD-1/PD-L1 and other associated genes linked to immune evasion [43,44,45,46,47,48]. The gene discussed is HDAC9; the disease is melanoma.