RRM2 and thyroid cancer: Over the years, studies continually found that RRM2 was overexpressed in various tumors, such as pancreatic cancer [15], neuroblastoma [16], thyroid malignant tumor [17], breast cancer [18], melanoma [19], lung cancer [20], prostate carcinoma [21], and hepatocellular carcinoma [22]; elevated RRM2 activity played a vital role in tumorigenesis, progression, and invasion and can serve as prognostic markers in some instances.