ME1-ANTIBODY LABELING OF PRIMARY BRONCHOGENIC TUMORS AND EXTRAPULMONARY MALIGNANCIES

ME1 is a monoclonal antibody which is generated by the use of a mesoth elioma cell line (SPCIII). The antibody has a preferential reaction to antigens on mesothelial and mesothelioma cells. In a prospective stud y we determined the reactivity in frozen sections from malignant mesot heliomas (two cases, positive controls), lung tumours (115 cases) and other malignant tumours (23 cases). The two malignant mesotheliomas we re immunoreactive in most of the tumour cells. The reaction was strong , often with a diffuse staining of the cytoplasm and in some tumour ce lls there was heavy staining of the cell membrane. Five adenocarcinoma s of the lung (9%), one large cell carcinoma (10%) and 18 squamous cel l carcinomas of the lung (41%) were positive (defined as tumours conta ining more than 10% positive tumour cells with a strong reaction). The same was true for seven out of 23 (30%) extrapulmonary malignancies. The overall nosologic specificity of ME1 was 76%. Twenty out of the 26 ME1-positive lung tumours and six out of seven ME1-positive extrapulm onary malignancies were also positive for one or more markers, which i s considered characteristic of carcinomas. The six negative lung tumou rs were squamous cells carcinomas and the negative extrapulmonary tumo ur was a meningeoma; all of them with a morphology different to malign ant mesothelioma. In conclusion, when frozen sections are available, M E1 might be useful in the differential diagnosis of malignant tumours. However, a positive reaction is not specific for malignant mesothelio ma.