Interestingly, previous studies have identified synergistic combination of LSD1 inhibitors and histone deacetylase (HDAC) inhibitors in multiple cancers.49,50 However, we failed to find this combination although TCP was individually testified with two common HDACi inhibitors (Trichostatin A, Panobinostat) in HNSCC. Here, HDAC9 is linked to head and neck squamous cell carcinoma.