CCNA1 and head and neck squamous cell carcinoma: However, several studies have shown that promoter methylation of CCNA1 had no effect on protein or gene expression in HPV-positive HNSCC in spite of a strong correlation between CCNA1 overexpression and HPV positivity, suggesting that HPV may induce both promoter hypermethylation and overexpression [47, 49, 50].