Human placental alkaline phosphatase in benign and malignant ovarian neoplasia.

In benign and malignant ovarian tumor patients, human placental alkaline phosphatase (HPLAP) was determined in serum and extracts from surgical tumor biopsies using a highly specific enzyme-antigen immunoassay based on a mouse monoclonal antibody (E6) to HPLAP. Serum HPLAP levels greater than or equal to 0.1 unit/liter were found in 58% of ovarian cancer patients. Serum carcinoembryonic antigen levels were positive (greater than 5.4 ng/ml) in 17% of these patients. HPLAP was detected in extracts from 13 of the 14 tumors investigated (range, 2.4 to 557 milliunits/g). Only the mixed heterologous Müllerian sarcoma was negative. The highest HPLAP content of normal ovarian tissue was 1.1 milliunits/g. The amount of heat-stable and L-p-bromotetramisole-insensitive alkaline phosphatase was in all cases much higher than the fraction recognized by E6. The neoplastic origin of HPLAP was confirmed immunohistochemically on paraffin sections by an indirect avidin-biotin-peroxidase staining procedure using E6. The staining pattern was compared to the histochemical distribution of total alkaline phosphatase on adjacent sections. A consistency was found between the amount of HPLAP in tissue extracts and its immunohistochemical distribution. In all the tumors, staining for HPLAP was observed mainly on the plasma membranes of carcinoma cells. In 9 of the 10 carcinomas, the histological distribution of HPLAP and also of total alkaline phosphatase was heterogeneous. HPLAP staining, present in one of five normal ovaries, was restricted to germinal inclusion cysts. The present results support the hypothesis that serous ovarian tumors originate from these cysts.

Enzyme-antigen immunoassay for human placental alkaline phosphatase in serum and tissue extracts, and its application as a tumor marker.

In this enzyme-antigen immunoassay for human placental alkaline phosphatase (hPLAP; EC 3.1.3.1.) in serum and tissue extracts, polyclonal rabbit antiserum to mouse IgG2b is adsorbed to the wells of a microtiter plate, its excess binding sites are blocked, then it is incubated with murine monoclonal anti-hPLAP and mixed with serially diluted standard or sample antigen. The amount of antigen bound is determined by measuring its enzymic activity. The standard curve is linear for hPLAP concentrations of 0.2 to 1 U/L. The mean within-assay CV was 3.8% (SD 0.9%) for a serum sample and 6.1% (SD 3.0%) for a tissue extract. The respective mean between-assay CVs were: 6.7% (SD 2.0%), and 7.0% (SD 2.0%). Serum hPLAP concentrations, determined in four different dilutions, had a CV of 5.5%. We evaluated the method by standard additions and by comparing dilution curves for purified hPLAP, hPLAP in serum, and hPLAP in tissue extracts. The upper limit of activity in normal subjects was 0.1 U/L for serum samples, and 1.0 mU/g wet weight of tissue for tissue extracts. hPLAP activity was increased in 9.8% of all cancer patients, and in 40% of ovarian cancer patients. Almost half of the tumor biopsies were positive for hPLAP activity, and 94% of the biopsies from ovarian neoplasia had an increased activity of this isoenzyme. Of the nonmalignant tissues examined, normal lung tissue had the highest hPLAP activity.