Immunohistochemical study of estrogen receptors in primary breast carcinomas and their lymph node metastases including comparison of two monoclonal antibodies.

Estrogen receptors (ER) status was investigated in 101 primary breast carcinomas and their axillary lymph node metastases to determine if the malignant cells retained or changed this phenotypic feature during the metastatic process. Immunohistochemistry with the ER-ICA kit (Abbott Laboratory) on formalin-fixed paraffin-embedded tissue was used (paraffin ER-ICA). The ER status in primary and secondary tumours was concordant in 80 patients (79%) and discordant in 21 (21%). Eighteen of these twenty-one patients had ER-positive primary tumours and ER-negative lymph node metastases. This discordance, which may be due to loss of ERs in the metastatic cells or tumour heterogeneity, could explain the well-known failure of endocrine treatment in some of the patients with ER-positive primary tumours. A new monoclonal antibody ID5 (DAKO) against ERs was applied on formalin-fixed paraffin-embedded tissue from 83 of these 101 primary carcinomas. These analyses and paraffin ER-ICA analyses were compared to prior analyses of the same 83 tumours using the ER-ICA kit on fresh frozen tissue ("gold standard", frozen ER-ICA). Kappa coefficient, sensitivity and specificity were 0.74, 0.96 and 0.75 for ID5 antibody, and 0.59, 0.72 and 0.96 for ER-ICA antibody on paraffin sections.