Fine‐needle aspiration cytology of pulmonary adenocarcinoma of fetal type: Report of a case with lmmunohistochemical and ultrastructural studies

This report describes the fine‐needle aspiration (FNA) cytology of a case of adenocarcinoma resembling fetal lung in a 53‐yr‐old male, a very uncommon malignant tumor of the lung that is similar to an early stage of lung differentiation. FNA smears revealed relatively small, fairly uniform tumor cells appearing as cohesive cell groups and scattered, isolated cells, some of them showing a rosette or acinus pattern. In addition, clusters of larger cells with eosinophilic cytoplasm and prominent nucleoli existed contiguously with the small cells or separately. The possibilities of an unusual type of adenocarcinoma, carcinoid tumor, and pulmonary blastoma were suggested by the cytologic findings. Immunohistochemical studies performed on a resected tumor tissue showed irnmunoreactivity for α‐fetoprotein, neuron‐specific enolase, and somatostatin, and endocrine‐type granules were found ultrastructurally. This type of adenocarcinoma is considered to have a histogenesis similar to that of pulmonary blastoma. To our knowledge this is the first reported case in the cytologic literature.