Our previous study evaluating a series of 50 novel ureido-sulfamate CAIX inhibitors, showed that 5 compounds could significantly inhibit proliferation of several human breast cancer cell lines in both hypoxic (0.5% O2) and normoxic conditions (21% O2); these were FC11409B, FC9398A, FC9403, FC9396A and S4 (24). This evidence concerns the gene CA9 and breast cancer.