Background: One of the most powerful tools used in “the team approach in modern medicine” is immunohistochemistry, a
minimally invasive investigative technique which is helpful in many respects, such as in suggesting or defining the primary site of metastatic malignant neoplasms. The panel of Cytokeratin7 (CK7), Cytokeratin20 (CK20) and Thyroid Transcription Factor-1 (TTF-1) is one of the most frequently used, and this study examined expressions of this panel in Rajavithi Hospital in order to assess their significance.
Objective: To study the expression of CK7, CK20 and TTF-1 in metastatic carcinoma in neck node biopsy found in the Rajavithi Hospital database, and to assess their effectiveness in identifying pulmonary origin.
Material and Method: The Rajavithi Hospital database was searched for all cases of lymph node biopsy in the neck and
supraclavicular area for which the pathological diagnosis was metastatic carcinoma. Expressions of CK7, CK20 and TTF-1 were analyzed to measure their sensitivity, specificity, positive predictive values, and negative predictive values.
Results: Average age of the subjects, of whom 56.9% were male, was 61.35+12.9 years. Lung (51.2%), breast (7.3%) and
gastrointestinal tract (6.5%) were the three most common organ site origins, and the most common cell type was
adenocarcinoma. Expressions are shown in terms of sensitivity (98.4%), specificity (95.0%), positive predictive value (95.4%), negative predictive value (98.3%) and others. The most reliable antibody for identification of pulmonary origin was TTF-1.
Conclusion: The immunohistochemistry panel of CK7, CK20 and TTF-1 in the Rajavithi Hospital database is useful as a guide in locating the origin of clinically unknown primary cases of metastatic cervical lymph nodes.

Keywords: Immunohistochemistry, Pulmonary origin, CK7, CK20, TTF-1, Rajavithi