With respect to the latter, the best studied in the context of cancer are the electroneutral Na+, HCO−3 cotransporter, SLC4A7 (NBCn1) and the Cl−/HCO−3 exchanger Down-regulated in Adenoma (SLC26A3, DRA): NBCn1 is upregulated in breast cancer and single-nucleotide polymorphisms (SNPs) in SLC4A7 have been linked to increased breast cancer risk while DRA, as the name implies, is essentially lost early upon transformation in many colorectal cancers, and is thought to function as a tumor suppressor. This evidence concerns the gene SLC4A7 and colorectal cancer.