CA9 and oral cavity squamous cell carcinoma: More intriguing is the data from Eckert et al. in oral squamous cell carcinoma [53], where patients with low coexpression of HIF-1α/CAIX indicated a good prognosis, whereas patients with increased HIF-1α and low CAIX expression had around 5-fold increased risk of tumor-related death (P = 0.042).