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 carcinom as. 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 m inus cell loss, the latter being achieved by apoptosis. At present, bc l-2 oncogene (apoptosis inhibitor) and p53 gene are assumed to be invo lved in the regulation of cell death and tumour proliferation. Sixty b reast carcinomas, initially indexed as medullary carcinomas, were re-c lassified using the diagnostic criteria given by Ridolfi. This review yielded 13 typical (TMC), 24 atypical (AMC), and 23 non-medullary carc inomas (NMC). Following antigen retrieval by microwave treatment, immu nohistochemical analyses, using MIB-1, p53 and bcl-2 monoclonal antibo dies were performed on serial sections from formalin-fixed, paraffin-e mbedded specimens. TMC revealed the highest incidence of intense p53 p ositivity, and the highest mean MIB-1 index, and absence of the apopto sis-inhibitor protein bcl-2. These results suggest the presence of a h igher overall cell turnover in TMC than in AMC and NMC. Increased apop tosis balancing the increased cell proliferation might be among the po ssible explanations for the more favourable prognosis in TMC.