CA9 and cancer: Interestingly, it was shown that CAIX work in support with diverse acid extruders such as MCT1 and MCT4 (109, 110), and as mentioned earlier, MCT-mediated H+ efflux exacerbates extracellular acidification and supports the formation of a hostile environment where cancer cells, that have adapted to these conditions, can outcompete normal cells, which further enhances tumor progression.