ALDH1A1 and head and neck squamous cell carcinoma: From the standpoint of CSC-related gene products, validated stemness gene-related proteins, such as Nanog and OCT4, support the invasive competence of tumor cells, which can self-renew.[48–50] Based on our data, overexpression of ALDH1, Nanog, and OCT4 was also found in long-term NNK- and arecoline-treated cells compared with the levels in control HNSCC cells.