CCND1 and oral cavity squamous cell carcinoma: Previous studies have shown that expression of PIS protein is increased in human head and neck squamous carcinoma cell lines and biopsy specimens from oral squamous cell carcinoma compared to normal cells and tissues, and inhibition of PIS induced G1 arrest in the cell cycle of oral cancer cells by reducing cellular levels of cyclin D1, cyclin E, and phosphorylated Prb67, 68.