A preferential selection of CAIX and GLUT-1 positive subclones in the primary tumor upon metastasis or adaptation to the local hypoxic environment may explain their negative to positive conversion in distant breast cancer metastases and might also explain the fact that GLUT-1 was positively associated with time to metastasis formation, as these processes might take time to develop and occur. Here, CA9 is linked to breast carcinoma.