A history of an increase in pulmonary mass was presented in the right upper lobe of a 72-year-old male. The bronchial brushing cytology specimens contained many sheet-like or three-dimensional clusters of malignant cells having small to medium-sized, uniform oval to round, and hyperchromatic nuclei, inconspicuous nucleoli, and scanty cytoplasm, admixed with mitotic figures. A coarsely granular chromatin pattern was predominantly noted. We first interpreted it as suspicious of malignancy, such as atypical carcinoid. A right upper lobectomy was performed, and gross examination revealed a centrally cavity-formed tumor lesion, containing asymmetrically thinned wall and looking grayish to whitish, partly adjacent to the bronchiolar wall. On microscopic examination, the tumor was predominantly composed of a solid proliferation of atypical epithelial cells without apparent glandular or squamous differentiation, often arranged in an alveolar growth pattern with peripheral palisading. Immunohistochemically, these atypical cells are negative for all three neuroendocrine markers and thyroid transcription factor 1, whereas positive for 34βE12, p63 and S-100 protein. Therefore, we finally made a diagnosis of basaloid carcinoma with cavity formation. We should be aware that, owing to its characteristic features, cytopathologists might be able to raise basaloid carcinoma of the lung as one of differential diagnoses, based on careful cytological examination.
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