IMMUNOHISTOCHEMICAL QUANTITATION OF ESTROGEN-RECEPTORS AND PROLIFERATIVE ACTIVITY IN ESTROGEN-RECEPTOR POSITIVE BREAST-CANCER

Aim-To evaluate the effect of the duration of formalin fixation and of tumour heterogeneity on quantitative estimates of oestrogen receptor content (oestrogen receptor index) and proliferative activity (MIB-1 i ndex) in breast cancer. Methods-Two monoclonal antibodies, MIB-1 and o estrogen receptor, were applied to formalin fixed, paraffin wax embedd ed tissue from 25 prospectively collected oestrogen receptor positive breast carcinomas, using a microwave antigen retrieval method. Tumour tissue was allocated systematically to different periods of fixation t o ensure minimal intraspecimen variation. The percentages of MIB-1 pos itive and oestrogen receptor positive nuclei were estimated in fields of vision sampled systematically from the entire specimen and from the whole tumour area of one ((representative)) cross-section. Results-No correlation was found between the oestrogen receptor and MIB-1 indice s and the duration of formalin fixation. The estimated MIB-1 and oestr ogen receptor indices in tissue sampled systematically from the entire tumour were closely correlated with estimates obtained in a ((represe ntative)) section. The intra- and interobserver correlation of the MIB -1 index was good, although a slight systematical error at the second assessment of the intraobserver study was noted. Conclusion-Quantitati ve estimates of oestrogen receptor content and proliferative activity are not significantly influenced by the period of fixation in formalin , varying from less than four hours to more than 48 hours. The MIB-1 a nd the oestrogen receptor indices obtained in a ''representative'' sec tion do not deviate significantly from average indices determined in t issue samples from Denmark the entire tumour. Finally, the estimation of MIB-1 index is reproducible, justifying its routine use.