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. This evidence concerns the gene CA9 and neoplasm.