CA9 and breast carcinoma: Another study using RCC4 renal clear cell carcinoma and MDA-MB-231 breast cancer cells indicated that STAT3 siRNA decreased the hypoxia-induced expression of HIF1-dependent genes such as pyruvate dehydrogenase kinase 1 (PDK1), angiopoietin-like 4 (ANGPTL4), carbonic anhydrase 9 (CA9), and HIF1/2-dependent VEGF [152].