MUC4 and breast cancer: In a preliminary screening of breast cancer cells, we observed that the invasive MDA-MB-231 TNBC cell line expressed MUC4 when grown in α-MEM media (Figure 1A, left lane), while non-invasive TNBC cell lines BT-20 and MDA-MB-468 [31] were MUC4 negative (data not shown).