Usefulness of immunocytochemistry for PAX8 for the diagnosis of carcinomatous pleuritis secondary to Napsin A-positive thyroid carcinoma

—A case report—

Abstract

We report the case of a 67-year-old male patient who presented with multiple pulmonary nodules and right pleural effusion 7 years after undergoing thyroidectomy for papillary carcinoma.

The effusion contained clusters of atypical cells which were immunocytochemically positive for Napsin A, as well as for TTF-1 and PAX-8. Re-evaluation of the primary thyroid carcinoma revealed Napsin A positivity in the cancer cells with focal squamous differentiation.

Napsin A is a useful marker of pulmonary adenocarcinoma ; however, caution is needed since some carcinomas in other organs could also express this marker. PAX-8 staining is useful to differentiate carcinomatous pleuritis secondary to Napsin A-positive thyroid carcinoma from that secondary to pulmonary adenocarcinoma.