To support and extend from evidence using 3D spheroid models, we analysed clonogenic survival (the gold-standard assay in radiobiology) of FaDu, along with two other HPV-negative HNSCC cell lines, A253 and UMSCC11b, in the presence of the HDAC inhibitors following increasing doses of X-rays. The gene discussed is HDAC9; the disease is head and neck squamous cell carcinoma.