Recurrent papillary thyroid carcinoma with pleural metastasis diagnosed by effusion cytology: a report of cases with clinicopathologic correlation.

Papillary thyroid carcinoma (PTC) is typically an indolent disease characterized by slow growth and a favorable prognosis. In rare instances, this disease may metastasize to the pleura and manifest as a malignant pleural effusion. We report 3 female patients of Japanese/Okinawan ancestry with a history of PTC who presented with hydrothorax. Cytologic examination in conjunction with immunohistochemical staining enabled a definitive diagnosis of metastatic PTC. Molecular analysis of the mitogen activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways demonstrated the presence of the v-raf murine sarcoma viral oncogene homolog B (BRAF)(V600E) mutation in 2 of our 3 patients, with the absence of any other clinically significant mutations in all cases. Further investigation is necessary to elucidate the molecular and environmental mechanisms involved in this aggressive manifestation of PTC.