Well-differentiated fetal adenocarcinoma of the lung: cytomorphologic features on fine-needle aspiration with emphasis on use of beta-catenin as a useful diagnostic marker.

Well-differentiated fetal adenocarcinoma (WDFA), also known as low grade adenocarcinoma of the fetal lung type, is a rare pulmonary neoplasm now considered to be a variant of lung adenocarcinoma rather than a type of pulmonary blastoma. Upregulation of the Wnt signaling pathway with subsequent aberrant nuclear/cytoplasmic beta-catenin expression has been recently described in these tumors providing a possible pathogenetic role for this gene in WDFA. We describe the cytomorphologic findings of a case of WDFA in a 36-yr-old female patient and emphasize the diagnostic utility of aberrant nuclear/cytoplasmic expression of beta-catenin as an adjunct to the correct preoperative recognition of this tumor on aspiration cytology.