Immunohistochemical detection of progesterone receptor in formalin-fixed and paraffin-embedded breast cancer tissue using a monoclonal antibody

The potential for immunohistochemical detection of progesterone receptors (PRs) in routinely formalin-fixed and paraffin-embedded cancer tissues by use of the monoclonal antibody Mi 60-10 (mPR1, Dianova GmbH, Hamburg) was evaluated. The PR content of breast cancer tissue was investigated in 170 cases. A positive reaction to Mi 60-10 was found exclusively in the nuclei of benign or malignant epithelial cells. The distribution of PRs was heterogeneous. Immunohistochemical reaction was scored by multiplying the percentage of positive tumour cells by their prevalent degree of staining (Immunoreactive Score or IRS). The IRS values of formalin-fixed tissues (n = 170) were compared with those in snap frozen tissues (n = 82), with the PR content assayed by a DCC (dextran-coated charcoal) method (n = 170), with histopathological grading according to Bloom and Richardson and with the menopausal status of the patient. There was an acceptable ranked correlation (r = 0.74) between IRS in formalin-fixed and paraffin-embedded parts and snap frozen parts of the same carcinoma. A good correlation (r = 0.72) was also found, when the semiquantitative results of immunohistochemical PR detection in formalin-fixed and paraffin-embedded tissues were compared to PR concentrations measured by a DCC method in tumor cytosols. There was an 80% concordance between the two methods for qualitative discrimination of PR-negative and PR-positive carcinomas. IRS correlated significantly with the degree of histological differentiation of the tumors (P less than 0.001) but not with the menopausal status of the women (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)