Carbonic anhydrase IX antigen differentiates between preneoplastic malignant lesions in non-small cell lung carcinoma

The MaTu interval (MN)/carbonic anhydrase (CA) IX tumour-associated antigen is a protein that is normally expressed in the gut and belongs to the carbonic anhydrase enzyme family (CA IX). It has been detected in tumour cell lines and in some solid tumours including cervical, oesophageal and clear cell renal carcinoma. This study determined MN/CA IX expression in 65 primary non-small cell lung cancer resected with curative intent and in 38 bronchial preneoplastic lesions, carcinoma in situ or microinvasive carcinoma as well as in normal bronchial tissue. The presence of MN/CA IX was detected using immunohistochemistry and Western blot analysis, whenever frozen material was available. Immunostaining was positive in 52/65 (80%) of the tumour samples. The staining was more often focal than diffuse. The percentage of stained cells in positive tumours was highly variable, ranging 1-85%. The pattern of immunostaining was predominantly cytoplasmic with a membranous reinforcement (87%). The intensity was mainly strong (69%). The presence of the protein in the tumour was confirmed by Western blot analysis in the eight samples tested. All the morphologically normal epithelia, except in close vicinity of tumours in some cases, as well as the preneoplastic bronchial lesions (basal cell hyperplasia, metaplasia and dysplasia) were immunonegative for MN/CA IX expression. In contrast, carcinoma in situ and microinvasive epithelioma showed the presence of MN-immunopositive tumoural cells in 5/7 and 4/5 of the samples, respectively. These data suggest that MN/CA IX is a useful marker for the differentiation between preneoplastic lesions and bronchial non-small cell lung cancer in the lung.