One study has suggested that MUC1expression follows the trend SK-BR3 < MDA-MB-231 ≤ MCF-7,albeit that there was significant variability between assay methods.In any case, discrimination between the breast cancer cells by thecombination of anti-HER2, anti-MUC1, and anti-ER was possible, withthe future potential for screening of breast cancer cell samples forclassification as luminal (A or B), HER2 enriched, and triple-negative. Here, ESR1 is linked to breast cancer.