MONOCLONAL-ANTIBODY PD-41 RECOGNIZES A PROSTATE-CANCER ASSOCIATED ANTIGEN WHOSE EXPRESSION INCREASES IN METASTASES AND FOLLOWING HORMONAL-THERAPY

Tissues of prostatic origin representing variable phenotypes were test ed for reactivity to the prostate cancer specific mouse monoclonal ant ibody PD-41. Avidin biotin immunoperoxidase was applied on formalin-fi xed, paraffin-embedded tissue sections of 15 benign prostatic hyperpla sia (BPH), 23 prostatic intraepithelial neoplasia (PIN), 14 untreated primary adenocarcinoma, 35 diethylstilbestrol (DES) treated tumors, 50 lymph node and 11 bone metastases. Specimens were stratified accordin g to the percentage of tumor cells expressing PD-41 antigen and degree of staining intensity, and correlated with PIN grade, Gleason score, flow cytometry (FCM) measured DNA ploidy, and reactivity to other anti bodies. In PIN, 4 specimens (17.4%) showed reactivity in a significant number of cells while a few cells were reactive in most cases. PD-41 was significantly reactive (>5% of tumor cells) in 88% of nodal metast ases and in 73% of bone metastases in contrast to 49% reactivity in pr imary tumors (p=0.0003). There was a tendency of increased antigen exp ression in hormonally treated primary tumors. In addition, involutiona l and metaplastic changes in hormonally treated cases were reactive in many instances. Semi-quantitative evaluation of PD-41 reactivity show ed a statistically significant correlation with Gleason score in prima ry tumors (p=0.007) and in lymph node metastases (p=0.009). Moreover, the PD-41 antibody reacted in metastatic lesions that failed to expres s both prostatic acid phosphatase and prostate specific antigen. These data suggest that monoclonal antibody PD-41 merits further investigat ion to evaluate its potential diagnostic, prognostic and therapeutic r ole in prostate cancer.