Metastatic papillary thyroid cancer misdiagnosed as non-small [corrected] cell lung cancer

Thyroid and lung cancers, two malignancies with similar immunohistological characteristics, have vastly different biologic behaviors and treatment approaches. As thyroid cancers commonly spread to the lungs, metastatic thyroid cancer should be included in the differential diagnosis of a pulmonary lesion or lesions.

A 54-year-old woman with a remote history of stage IV nonsmall cell lung cancer was found to have FDG avidity in the thyroid and right cervical lymph nodes. Subsequent ultrasonographic findings and FNA cytology led to a total thyroidectomy, bilateral central lymphadenectomy, and right modified radical lymph node dissection for primary thyroid cancer. Reviews and comparisons of the pulmonary and cervical surgical specimens revealed that the patient had been misdiagnosed for the previous 6 years; she had metastatic papillary thyroid cancer to the lung. The patient's original diagnosis of stage IV lung cancer was based upon the original lung biopsy showing positive thyroid transcription factor-1 (TTF-1) immunostaining. The original diagnosis was questioned because of her long survival when she was diagnosed with locally advanced papillary thyroid cancer. Further analyses of the immunohistological characteristics of both surgical specimens--including staining for TTF-1, thyroglobulin, CD57, S-100, and CEA--documented the correct diagnosis.

A thorough understanding of the natural history and surgical pathology, including immunohistology, of lung and thyroid cancers is necessary for a correct and timely diagnosis and appropriate treatment. Because TTF-1 expression is seen in both thyroid and lung cancers, careful consideration should be given to both malignancies when evaluating patients with thyroid and pulmonary nodules.