Immunocytochemical detection of progesterone receptor in breast cancer with monoclonal antibody. Relation to biochemical assay, disease-free survival, and clinical endocrine response.

A new immunocytochemical assay for progesterone receptor (PgR-ICA) employing the monoclonal antibody JZB 39 was used to study tumors from two series of patients with breast cancer. In Series 1 assay results were in agreement with those of biochemistry in 76% of 338 cases (P less than 0.001) and in 54% of 101 cases in Series 2 (P less than 0.001). Agreement was better in Series 1 because it included fresher, previously untouched specimens. There were 70 patients in Series 1 with known clinical endocrine response. A negative assay correlated with disease progression in 45 of 57 patients, significantly better than with biochemistry (P = 0.013). In comparing 39 women with rapid disease progression with 39 free of disease at 5.1 years, those with PgR-ICA-positive tumors were over four times more likely to remain disease-free than those with negative results (P = 0.007). Product moment life-table analysis of 79 patients from Series 2 showed a significantly better cumulative survival for those with PgR-ICA-positive tumors (P = 0.047). These findings indicate that PgR-ICA should be of value in planning therapy and predicting disease course in breast cancer patients.