MIB-1 expression in breast carcinomas with medullary features. An immunohistological study including correlations with p53 and bcl-2.
Typical medullary carcinoma (TMC) is usually considered to have a more favourable prognosis than other types of infiltrating breast carcinomas. This is a biological paradox, since its clinical behaviour is not in agreement with its anaplastic morphology and high mitotic rate. It should be remembered that neoplastic growth reflects cell production minus cell loss, the latter being achieved by apoptosis. At present, bcl-2 oncogene (apoptosis inhibitor) and p53 gene are assumed to be involved in the regulation of cell death and tumour proliferation. Sixty breast carcinomas, initially indexed as medullary carcinomas, were re-classified using the diagnostic criteria given by Ridolfi. This review yielded 13 typical (TMC), 24 atypical (AMC), and 23 non-medullary carcinomas (NMC). Following antigen retrieval by microwave treatment, immunohistochemical analyses, using MIB-1, p53 and bcl-2 monoclonal antibodies were performed on serial sections from formalin-fixed, paraffin-embedded specimens. TMC revealed the highest incidence of intense p53 positivity, and the highest mean MIB-1 index, and absence of the apoptosis-inhibitor protein bcl-2. These results suggest the presence of a higher overall cell turnover in TMC than in AMC and NMC. Increased apoptosis balancing the increased cell proliferation might be among the possible explanations for the more favourable prognosis in TMC.