MUC4 and neoplasm: Consistent with a previous report that concluded that MUC4 is expressed in 95% of breast cancers on the basis of immunohistochemical staining [23], we detected the presence of the MUC4β band of about 100 kDa in 59 of 70 (84%) of tumors (Figure 2), although the relative levels of MUC4β protein varied considerably among tumor samples.