Medullary breast carcinoma vs. poorly differentiated ductal carcinoma: an immunohistochemical study with keratin 19 and oestrogen receptor staining.

Sixty breast carcinomas previously indexed as medullary carcinomas over a 24-year-period were reviewed and reclassified according to definitions suggested by Ridolfi et al. as typical medullary carcinoma, atypical medullary carcinoma, and non-medullary carcinoma. Paraffin sections of tumour tissue were examined by an avidin-biotin complex method using two keratin 19-specific monoclonal antibodies (BA17, DAKO and clone 170-2-14, Boehringer) and a monoclonal oestrogen receptor antibody (DAKO). For comparison 52 ductal carcinomas of grade II and grade III were immunostained as well. The results showed that all 60 tumours with medullary features and all 52 ductal carcinomas reacted moderately to strongly positive with anti-keratin 19 (Boehringer). The staining was diffuse in all cases, except one case of ductal carcinoma (grade III), which stained focally. Immunostaining with the second keratin 19 antibody (BA17) revealed similar results with positive staining in 59 (95%) cases of carcinomas with medullary features and 51 (98%) cases of ductal carcinomas. Only one case in each group did not express keratin 19 (BA17), one re-classified case of non-medullary carcinoma with neuroendocrine features and one case of ductal carcinoma of grade III. None of the 13 cases of typical medullary carcinoma were oestrogen receptor positive and only seven (12%) of the carcinomas with medullary features (2 atypical, 5 non-medullary) were oestrogen receptor positive with quantitative values from 20 to 100%. The 52 ductal carcinomas of grade II and III were oestrogen receptor positive in 56% and 47% of cases. It is concluded that keratin 19 staining is of no particular value in differentiating medullary from poorly differentiated ductal carcinoma. A carcinoma with positive oestrogen receptor staining is not likely to be a typical medullary carcinoma.