FANCD2 and esophageal squamous cell carcinoma: To compare the functional impact of POLQ single KO, FANCD2 single KO, POLQ/FANCD2 double KO and the control ESCC cells, we constructed the FANCD2 KO (FANCD2KO) and POLQ/FANCD2 KO (DK) ESCC cell lines.