SPHK1 and head and neck squamous cell carcinoma: The same results were observed for the relationship between SPHK1 and immune checkpoints and immune-infiltrating cells in TCGA (The Cancer Genome Atlas) dataset of patients with HNSCC (Figure S1B-C), and SPHK1 expression was inversely associated with overall survival (OS) and disease-free survival (DFS) (Figure S1D).