CD34 and cancer: Specifically, the mucin MUC1 has been shown to express TF-Ag in breast [14] and colon [6] while MUC4 in pancreatic [7] cancer; CD44 has been identified as a major TF-Ag carrier in colon cancer [15]; in cancers of lung, breast, and liver CD133 and CD44 express TF-Ag [16]; and CD34 was shown to express TF-Ag on malignant hematopoietic cells [17].