SLC22A15 encodes a solute carrier which has recently been de-orphaned and shown to have a specificity for zwitterions such as carnosine, ergothioneine and betaine [32], Little is known about its normal physiological roles, although a recent study has suggested a key role in controlling carnosine availability in the brain [33] and several studies have identified carnosine as a metabolite that shows anti-tumour activity against multiple different cancers [34–36]. Here, SLC22A15 is linked to cancer.