Lung adenocarcinoma and its thyroid metastasis characterized on fine-needle aspirates by cytomorphology, immunocytochemistry, and next-generation sequencing.

Lung adenocarcinoma and papillary thyroid carcinoma (PTC) share a number of microscopic and immunophenotypical features. Thus, patients presenting with thyroid and lung synchronous neoplasms may be difficult on fine-needle aspiration (FNA) samples to define the site of origin of the malignancy. In the case reported here, inherent to a 57-years-old man presenting with a right lung mass and a large (44 mm) thyroid nodule, an integrated cytological, immunocytochemical and molecular approach enabled to clarify the primary nature of the neoplasm. FNA cytology showed in both sites papillary structures and nuclear changes reminiscent of PTC. The lung origin of the neoplasm was suggested on cell-block immunocytochemistry showing thyroid transcription factor-1 positive and PAX8 and TGB negative neoplastic cells. Next generation sequencing performed on the Ion Torrent platforms by the Ion Ampliseq Colon and Lung Cancer panel showed a similar genomic profile in both neoplastic sites with a concurrent KRAS G12C mutation. An integrated approach on FNA biospecimen is safe, cost effective, and may be coupled effectively with modern ancillary molecular techniques that may be useful, besides their predictive value, as a adjunctive diagnostic tool when the synchronous occurrence of lesions featuring overlapping morphologies challenge the cytopathologist.