Mucin expression by transitional cell carcinomas of the bladder

OBJECTIVE: To examine the presence of a membrane-associated and secreted mucin (MUC1) and a secreted gel-forming mucin (MUC2) in normal and malignant urothelium. MATERIALS AND METHODS: Sections were obtained from archival paraffin blocks from 11 patients with nonmalignant urological conditions and 89 patients with transitional cell carcinomas (TCC). Mucin expression was examined by immunohistochemistry using monoclonal antibodies BC2 and 4F1, reactive with epitopes on the protein core of MUC1 and MUC2 respectively. RESULTS: In normal urothelium MUC1 was limited predominantly to the apical membranes of the umbrella cell layer. MUC1 was present in all cases of TCC, and the pattern of expression divided into three categories: luminal membrane staining only, luminal plus cytoplasmic staining of intermediate +/- basal layers, or staining of only isolated cells or cell groups. These staining patterns were significantly associated with both tumour grade and stage (P < 0.001), with cytoplasmic staining more prevalent in higher grade and stage tumours. MUC2 was not detected in normal urothelium, and was present in 40% of cases of TCC, characterized by intense granular cytoplasmic staining. No association between MUC2 expression and either tumour grade or stage was demonstrated. CONCLUSION: MUC1 mucin was expressed by both normal and malignant urothelium, with increased expression characteristic of higher grade and stage tumours. MUC2 expression was found in 40% of tumours but not in normal urothelium. The role of these mucins in the biology of the bladder requires further investigation.