Diagnostic histochemical and immunohistochemical studies in malignant mesothelioma

This study was undertaken to evaluate the relative utility of histochemical and immunohistochemical stains in diagnosing malignant mesothelioma of the thorax. We performed a battery of histochemical stains, including periodic acid Schiff (PAS) with and without diastase, mucicarmine, colloidal iron (Coll Fe) with and without hyaluronidase, and immunohistochemical stains for keratin and carcinoembryonic antigen (CEA) on 12 pleural mesothelioma specimens obtained from 11 patients, five primary pulmonary adenocarcinomas, and one metastatic adenocarcinoma each to pleura and pericardium. All diagnoses were established by autopsy or thorough clinical and surgical evaluation. The diagnosis of mesothelioma was established following rigid anatomic criteria. All tissue was formalin fixed and paraffin embedded. Commercially available reagents and antisera were used in all cases. Results showed a high rate of positivity for keratin and hyaluronidase-sensitive Coll Fe in the mesotheliomas while adenocarcinomas were uniformly positive for CEA and keratin and generally positive for PAS-D (diastase) and mucicarmine. Mesotheliomas were negative for CEA, mucin, and PAS-D. Positive keratin staining was also seen in the spindle cell components of mesotheliomas. Immunohistochemical stains often added significantly to our ability to establish the diagnosis of mesothelioma with confidence, since they were more frequently and more clearly positive than histochemical stains.