MUC1 and breast adenocarcinoma: Finally, MDA-MB-231 cells, a breast adenocarcinoma cell line negative for the expression of the MUC1-Tn antigen, were not very sensitive to GRNLY, and this cytotoxicity did not increase when using AR20.5GRNLY, confirming the usefulness of this cell line as a negative control for MUC1-Tn expression.