Importance of immunohistochemistry and application of TTF-1 and napsin A in differential diagnosis of primary pulmonary adenocarcinomas and pulmonary metastases of extrapulmonary origins

The differential diagnosis between primary and secondary pulmonary adenocarcinomas is daily requisition for pathologist. Lungs are the most common site of metastases from various primary and primary pulmonary adenocarcinomas are one of the most common worldwide malignancies. Immunohistochemistry is useful method to determine the origin of tumor in case when histomorphology alone is insufficient in poor differentiated carcinomas. Accordingly, presence of enteric, clear cell, spindle cell and signet-ring cell features complicates determining of origin of adenocarcinomas. The most common and long-used lung specific immunohistochemical marker is TTF-1, but specificity and sensitivity is not 100%. Use of TTF-1 has pitfalls that complicate its routine use. TTF-1 alone is insufficient marker for determining of origin of adenocarcinoma in the lung. Newly used immunohistochemical marker is napsin A. According to many authors is sensitivity and specificity for napsin A higher than TTF-1. Use of TTF-1 and napsin A simultaneously increases sensitivity up to 85% for primary lung adenocarcinomas. Both immunohistochemical l markers can be expressed in various tumours of extrapulmonary origin that can metastasize to lung, thus specificity is not 100%. In cases of surgical resection of tumor wider panels of immunohistochemical antibodies are used. Small biopsies and cytological material is quantitative restricted and sometimes qualitatively deficient. It is sometimes complicated and even impossible for pathologist to determine primary origin of tumor. (author)