CA9 and neoplasm: To determine whether HIF-1 accumulation triggers a transcriptional response, using TaqMan RT-qPCR, we have studied the mRNA expression level of Carbonic Anhydrase IX (CAIX) in parallel to PFKFB4. CAIX is a HIF-1 target gene [17,18] and expression of this gene in many types of tumors indicates its relevance as a general marker of tumor hypoxia [19].