HHLA2 and oral cavity squamous cell carcinoma: In colorectal cancer, HHLA2 is expressed more prominently in the tumor than in healthy tissues, and similar tendencies can be observed in clear cell renal cell carcinoma, hepatic malignancies, gallbladder cancer, oral squamous cell carcinoma, lung cancer, bladder urothelial carcinoma, and thyroid cancer [13,23,25,28,36,46,48,49,66,67,72,84].