Immunocytochemical determination of the estrogen-regulated protein Mr 24,000 in primary breast cancer and response to endocrine therapy.
Monoclonal antibodies against an estrogen-regulated Mr 24,000 cytosol protein (p24) were used for immunocytochemical localization of p24 in formalin-fixed paraffin-embedded specimens from the primary tumor in 103 patients who received endocrine therapy for advanced breast cancer. Sixty-one per cent of the tumors showed p24-positive staining, and this correlated well with the presence of estrogen receptor (ER) (P = 0.00017, chi-square test). Response to endocrine therapy was obtained in 43% of the patients. A statistically significant association between p24 status and response could not be established, while response and ER status were highly correlated (P = 0.0000029, chi-square = 21.6). Discrimination between ER-positive responders and ER-positive non-responders was not possible using p24 staining.