Summary: A monoclonal antibody (NDOG2) against placental alkaline phosphatase (PLAP) in ovarian cancer has been used in three ways by the Bristol University Department of Obstetrics & Gynaecology. First, in an indirect immunoperoxidase technique, NDOG2 demonstrated positive standing in 64% of 56 ovarian carcinomas as well as in 25% of 44 benign tumours. The majority of these positive tumours were serous cystadenocarcinomas or serous cystadenomas and there was considerable variation in the expression of this antigen from tumour to tumour. NDOG2 was also used as the basis of two serum assays and, when labelled with 123-iodine (1231), in radioimmunoscintigraphy (RIS) to monitor patients' response to therapy. The first serum assay measures the enzymic activity of PLAP and the second recognizes the antigenicity of the molecules. Assay 2 proved more useful in that it predicted the course of the disease in 45% of patients followed up, whereas Assay 1 was only of use in 25% of cases. RIS proved to be a useful imaging technique and was at least as sensitive as conventional imaging techniques. The common causes of false-positive and false-negative results are described. IntroductionOvarian cancer is the most commonly occurring gynaecological malignancy in the United Kingdom (OPCS 1983) and, because of its propensity for intra-abdominal metastasis, presents particular problems in assessing a patient's response to therapy. In addition, it is a cancer that

The presence of placental alkaline phosphatase has been demonstrated immunohistochemically using a monoclonal antibody, in frozen sections of human endometrium. The enzyme is present in glandular epithelium, but is found most commonly in the surface epithelial layer throughout the menstrual cycle. It has also been demonstrated in malignant endometrial epithelium in eight out of twelve patients.

A radiolabelled monoclonal antibody (NDOG,) dircctcd against placental alkaline phosphatasc (PLAP) was used in the radioimmunodetection of ovarian carcinoma. Tumour deposits were successfully visualized in 11 of 15 patients and the abnormalities demonstrated were classified as focal or diffuse. Of the 11 patients, eight showed focal abnormalities alone a n d three had a diffuse abnormality, of which two also showed a focal abnormality. False-positive results may occur not only due to uptake of lz3I by gut mucosa and an inadequately blocked thyroid gland but also from activity in an incompletely emptied bladder. A false-negative result occurred due to high background activity in the liver macking a known, discrete tumour deposit.

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