In fact, the role of PDE5 inhibition in augmenting both the general and tumor-specific immune response in HNSCC was further confirmed by two randomized, double-blinded, placebo-controlled clinical trials (NCT00894413 and NCT00843635) that used tadalafil for PDE5 inhibition [53,54]. The gene discussed is PDE5A; the disease is head and neck squamous cell carcinoma.