Expression of vitamin B12 R-binder in breast tumors. An immunohistochemical study

Vitamin B12 R-binder, a vitamin B12-specific binding protein, was demonstrated by immunohistochemistry in 103 cases of breast tumors of various types and grades. In normal breast tissues, R-binder was found on the luminal surface of interlobular, intralobular, and small terminal ducts. R-binder localization was observed in all fibroadenomas and phyllode tumors, in 90% of the benign epithelial tumors, and in 33% of the carcinomas. Among malignant tumors, 43% of the ductal carcinomas expressed the R-binder, whereas none of the lobular or mucinous carcinomas were positive. In invasive ductal carcinomas, R-binder expression was demonstrated more often in well-differentiated lesions.