CA9 and breast cancer: Based on our findings, we demonstrated in this study that A6 (N-(4-sulfamoylphenyl)-1H-indole-5-carboxamide) and A15 (N-(1H-indol-5-yl)-4-sulfamoylbenzamide) suppressed tumor growth and cell migration of MCF-7 and SK-BR-3 cells through inhibition of CA IX, and the combination of these compounds with DOX exhibited synergistic cytotoxic effects on these breast cancer cells.