Diagnostic value of immunohistochemically detected surfactant--apoprotein-A in malignant tumors located in the lungs: report of two cases.

We report two cases of patients suffering from multiple tumors in the lungs with questionable origin. In these cases, the expression of Surfactant-apoprotein-A (SP-A) by the tumor cells has been a helpful feature in the process of diagnosis by indicating primary carcinomas of the lungs. Surfactant-apoprotein-A is expressed by the pneumocytes II in lung tissue and a portion of non-small cell lung carcinomas and has not yet been found to be expressed by other tumors when detected immunohistochemically by use of the monoclonal antibody PE-10. We analyzed formalin-fixed, paraffin-embedded specimens of different malignancies with pulmonary location for the expression of SP-A by the use of PE-10 with other antibodies against additional epitopes such as the thyroid transcription factor-1. In normal lung areas a distinct staining of the pneumocytes II has been observed. All the control sections of primary and metastatic nonlung-carcinoma specimen in our study remained negative. The monoclonal antibody PE-10 used in this study provides high specificity when compared to the results obtained with polyclonal antibodies. One of the two cases reported, a mucinous carcinoma of the lungs, had been negative for thyroid transcription factor-1 but positive for SP-A. Thus, SP-A detected by immunohistochemistry using the monoclonal antibody PE-10, together with other parameters such as thyroid transcription factor-1, may be a useful tool for individual diagnosis of malignomas located in the lungs with a questionable primary origin. Ann Diagn Pathol 5:84-90, 2001.