PLAC1 and head and neck squamous cell carcinoma: In addition, an IHC assay was performed to validate the SP1 expression pattern in clinical tumor tissues and we observed a robust positive correlation between SP1 IHC scores and plac1 IHC scores (R = 0.419, p = 0.0022), which further supported our hypothesis that SP1 could induce Plac1 expression during HNSCC initiation and progression (Figure 2J,K).