Neither calretinin nor HBME-1 are sufficiently discriminatory to be of use, even as members of a panel of antibodies. WT1 shows some promise, but it cannot be used on autopsy material. The utility of MOC-31 is confirmed, and outperforms Leu-M1.

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We conclude that this antibody is potentially a useful positive marker for the identification of the epithelioid variant of mesothelioma in formalin-fixed and paraffin-embedded material.

Aims-To investigate the reaction of antibodies OV 632 and MOC 31 in paraffin wax sections as opposed to frozen sections and cytological preparations; to evaluate their usefulness in the differential diagnosis of malignant mesothelioma and secondary adenocarcinoma ofthe pleura; and to assess the efficacy of microwave pretreatment of sections in unmasking their associated epitopes. Methods-Immunohistochemistry, using a standard avidin-biotin technique, with microwave pretreatment and trypsinisation in a certain proportion of cases. The material comprised 43 mesotheliomas, 44 adenocarcinomas and five reactive pleuras. Results-Epithelial mesotheliomas and the hyperplastic mesothelial cells reacted strongly with OV 632, the reaction with sarcomatoid and desmoplastic tumours was weak, and the reaction with adenocarcinomas was variable. An unequivocal but sometimes patchy positive reaction was obtained with MOC 31 in all but one of the adenocarcinomas; all but one of the mesotheliomas and all the reactive pleuras were negative. Review ofthe two apparently anomalous cases revealed that the original diagnoses had probably been incorrect. Reactions to both antibodies were abolished by microwave pretreatment, and also by prior trypsinisation in the case of OV 632. Conclusions-OV 632 is unsuitable for routine clinical use in paraffin wax embedded material. MOC 31, however, would be a useful addition to a panel ofantibodies in the differential diagnosis of mesothelioma and adenocarcinoma in large biopsy and resection specimens and necropsy material. Its value in small biopsy specimens remains to be assessed. Microwave pretreatment does not enhance the reactions with either antibody. (J7 Clin Pathol 1995;48:626-630) Keywords: OV 632, MOC 31, adenocarcinoma, mesothelioma.The differentiation between adenocarcinomatous infiltration of the pleura and mesothelioma is often difficult, particularly in small biopsy specimens. Conventional stains for epithelial and connective tissue mucosubstances can be helpful, but lack specificity,'2 and although long microvilli are almost pathognomonic of mesothelioma, material for electron microscopy is frequently unavailable. For some years now, immunocytochemical methods have been employed, using a variety of antibodies.`Unfortunately, no single antibody is wholly specific: vimentin and keratins are expressed by both carcinomas and mesotheliomas; LEU Ml is not expressed by mesothelioma, but a significant proportion of adenocarcinomas are also negative; and although mesothelioma is usually negative for carcinoembryonic antigen (CEA), non-specific cross reactions frequently occur.356 Because of the lack of specificity of both immunocytochemical and conventional histochemical reactions, it is now common practice to use a battery of tests.35-In a recent study,5 the best combination of two markers was found to be CEA and B72-3 (both positive; 100% specific and 88% sensitive for adenocarcinoma; both negative: 99% specific and 97% sensitive for mesothelioma). These results are encouraging, ...

The pathology of the lung in byssinotics. A report of the gross and microscopic appearances in the lungs and the weights of the cardiac ventricles in 43 subjects receiving industrial benefit for byssinosis is presented. In 27 (63%) there was no significant emphysema, in 10 (23%) there were varying amounts of centrilobular emphysema, and panacinar emphysema was found in six (14%). Other changes were of a non-specific nature, but most cases showed heavy black dust pigmentation, often associated with centrilobular dilatiation of distal air spaces.On microscopic examination the parenchyma showed no excessive fibrosis, granuloma formation or any other lesion to suggest an extrinsic alveolitis. The vasculature was in no way remarkable. Using a point-counting technique it was found that there was mucous gland hyperplasia and hypertrophy of smooth muscle in the upper and lower lobar bronchi but not to any significant degree in the segmental bronchi. These appearances suggest an irritant or pharmacological action on the larger bronchi rather than an allergic alveolitis or asthma. 'Byssinosis bodies' were found in seven cases, but the significance of these is doubtful.Comparison of the ventricular weights with 100 unselected cases coming to necropsy at the East Birmingham Hospital did not indicate an increased incidence of systemic or pulmonary hypertension in byssinotic subjects.