Fine needle aspiration cytology of pulmonary papillary adeno-carcinoma mimicking papillary thyroid carcinoma

We report a case of primary pulmonary papillary adenocarcinoma demonstrating classic nuclear and architectural features of papillary thyroid carcinoma including nuclear pseudo-inclusions, intranuclear grooves in the tumour cells nuclei, ground glass nuclei, papillary architecture with true fibrovascular cores lined by cuboidal cells with oval nuclei. Immunohistochemical staining was performed on cell block and the preparations showing the lesional cells to be positive for TTF-1, Napsin A and negative for Thyroglobulin and PAX8. The appearances and immunophenotype were consistent with a primary pulmonary papillary adenocarcinoma and excluded a metastasis from the thyroid. Awareness of the existence of PTC- like pulmonary papillary carcinoma along with use of immunohistochemistry can avoid misdiagnosis or unnecessary clinical and radiologic investigation.