The contribution of the basigin Ig-I domain to MCT-facilitated lactate/H+ transport is of (patho-)physiological relevance, as shown by a study that identified a transmembrane protease that is expressed in human lung squamous cell carcinomas and cleaves off the extracellular domain of basigin (Figure 2, right) [42]. This evidence concerns the gene BSG and squamous cell lung carcinoma.