PIK3CD and head and neck squamous cell carcinoma: A bioinformatics-based study showed that miR-99a-5p is downregulated in HNSCC and is negatively associated with expression of PIK3CD (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit delta), which takes part in the PI3K-Akt signaling pathway, suggesting that it may be a tumor suppressor in head and neck cancer (Chen et al. 2018).