Immunohistochemistry (IHC) staining showed that the expression level of ALDH7A1 was lower in the short-term PMS HNSCC patients carrying an ALDH7A1 mutation (missense, c.1168 G > C, rs121912707) than in the long-term PMS HNSCC patients carrying wild-type ALDH7A1 (ALDH7A1 normal expression) (Fig. 5b). Here, ALDH7A1 is linked to head and neck squamous cell carcinoma.