CA4 and breast cancer: Human and murine breast cancer tissue and corresponding normal breast tissue express transcripts for multiple carbonic anhydrase isoforms (Fig. 1B-D) with known localization in the cytosol (CA1, CA2/Car2, CA3/Car3, CA7/Car7, CA13/Car13), mitochondria (CA5A, CA5B/Car5b), and extracellular space either membrane-tethered (CA4/Car4, CA9/Car9, CA12/Car12, CA14/Car14, Car15) or secreted (CA6/Car6).