To investigate the role of COSMC in Tn expression, 40 cases of primary breast cancer were stained with antibodies to MUC1 (HMFG2), MUC1-Tn/STn (5E5) and MUC1-T (1B9), see S1 Table for the results of the individual tumors. This evidence concerns the gene MUC1 and breast carcinoma.