Changes in immunohistochemical staining in prostatic adenocarcinoma following diethylstilbestrol therapy

Twenty-eight pretreatment and posttreatment biopsies from 11 cases of prostatic adenocarcinoma were stained for prostate-specific acid phosphatase (PAP), prostate-specific antigen (PSA), and keratin to determine the effect of hormonal (diethylstilbestrol) therapy on these immunological markers. Treatment intervals ranged from 2 to 63 months. All pretreatment tumors were strongly positive for PAP, and nine were strongly positive for PSA. Two were weakly positive for PSA, and all were negative for keratin. In five of the 11 posttreatment group cases, staining with both PAP and PSA was reduced. In three posttreatment cases, the malignant epithelium showed a squamoid appearance, and in these areas the keratin gave a positive reaction. These findings indicate that immunohistochemical staining with PAP and PSA may change in response to hormonal therapy. These alterations may lead to false-negative results when using these techniques to identify the primary tumor source of metastatic deposits of prostatic carcinoma.