Immunohistochemical study of D5 antigen (an oestrogen receptor related protein) in normal breast, benign breast disease, and mammary carcinoma in situ.

Patterns of staining with a monoclonal antibody which recognises D5 antigen (a 29,000 kD oestrogen receptor-related protein) were studied in seven normal and 76 benign breast biopsy specimens as well as in 12 cases of pure in situ mammary carcinoma. Staining in benign breast lesions was weak and heterogeneous when compared with that seen in most infiltrating carcinomas. In situ carcinomas showed an intermediate pattern of staining. The finding of only small foci of weak positivity for D5 antigen in normal and benign breast disease indicated that there are similarities between the expression of D5 antigen and the presence of oestrogen receptor protein in these tissues. A further similarity was seen with in situ carcinomas, which have been shown to have lower oestrogen receptor content than infiltrating carcinomas and a more heterogeneous staining pattern with D5 than is seen in infiltrating tumours. The importance of these findings remains to be evaluated because the precise nature of D5 antigen and its association with the oestrogen receptor molecule is not fully understood.