ESR1 and squamous cell carcinoma: For experiments, the investigators used five cell lines: squamous carcinoma cell lines ME-180 (HPV-68 and ERα-positive) and CaSki, adenocarcinoma cell lines HCA-1 (ERα-positive) and HeLa, along with normal endocervical columnar cell line NCC16-P11 immortalized by HPV-16.