HHLA2 and thyroid cancer: By retrieving data from multiple databases, it was found that the expression level of TMIGD2, a costimulatory receptor of HHLA2, in thyroid cancer is higher than that in normal thyroid tissue, and its expression level affects the malignancy of thyroid tumors and even increases their adverse prognosis (Janakiram et al. 2015, Zhang et al. 2023).