ESR1 and head and neck squamous cell carcinoma: First, A20 overexpression was found in undifferentiated nasopharyngeal carcinoma, poorly differentiated head and neck squamous cell carcinomas (SCCs) of the skin, estrogen receptor (ER)-negative breast cancer cell lines, tamoxifen resistant ER-positive tumors, and hepatitis B virus-related hepatocellular carcinoma[32].