Evaluation of PAS-diastase and carcinoembryonic antigen staining in the differential diagnosis of malignant mesothelioma and papillary serous carcinoma of the ovary

A series of malignant mesotheliomas and papillary serous carcinomas of the ovary were stained using the periodic acid Schiff reaction with diastase digestion (PAS-D) and an immunoperoxidase technique for carcinoembryonic antigen (CEA). The methods were evaluated in terms of repeatability and validity. Staining reactions were classed as positive or negative by three 'blinded' observers. Within-observer repeatability was greater for PAS-D than for CEA but there was no statistically significant difference for between-observer repeatability. The validity of the methods clearly differed, however, since the sensitivity and specificity of CEA were consistently less than that of PAS-D. Our most consistent estimates of sensitivity and specificity were compared with those of other studies and the reasons for this difference were analysed. Positive PAS-D and CEA staining were uncorrelated but a combination of the two did not appear significantly superior to PAS-D alone. We believe that PAS-D remains the method of choice for differentiating peritoneal mesotheliomas and disseminated papillary serous carcinoma of the ovary in the absence of reliable evidence of an ovarian primary because the significance of CEA positivity in occasional mesothelial tumours remains to be determined.