While compound 9 was also the most potent hybrid ligand in the antiproliferative assay at ER-positive MCF-7 cells indicating that its anticancer action is mediated through binding to ERs, the gefitinib hybrids 6a and 6b were more potent at triple-negative breast cancer cells suggesting an ER-independent mechanism of action. Here, ESR1 is linked to triple-negative breast carcinoma.