POLA2 and esophageal squamous cell carcinoma: Single nucleotide polymorphisms (SNP) in genes, such as ALDH7A1 [81], POLA2 [82], LIG1 [83], and ERCC6L [84], are important for the development of various cancers, such as esophageal squamous cell carcinoma, lung cancer, and oral cancer, but these polymorphic genes may be linked with pathogenesis of BRCA.