The results of the present study are in accordance with previous studies reporting decreased abundances of Cystatin S, Cystatin-SA, and Cystatin-SN in unstimulated saliva of head and neck cancer patients 3–4 months post-treatment [18] and decreased levels of Cystatin D, S, SA, and SN in stimulated saliva at ≥ 6 months post-treatment [22]. This evidence concerns the gene CST4 and head and neck cancer.