Pleomorphic Carcinoid: A Pitfall in Diagnosis on Small Biopsy Specimens

Abstract Typical and atypical carcinoids account for 2% of all pulmonary neoplasms and are usually diagnosed based on characteristic neuroendocrine granules, architecture, and overall bland cytomorphology. However, there are rare carcinoids with unusual morphology mimicking features seen in non–small cell lung carcinoma, which can be a significant challenge on small biopsy or cytology specimens with major therapeutic implications. We report a case of a transbronchial needle aspirate that was initially misinterpreted as non–small cell lung carcinoma due to the presence of cohesive clusters of tumor cells showing striking pleomorphism and prominent nucleoli in a background of necrosis. In addition, tumor cells showed multifocal brown cytoplasmic melanin pigment that has rarely been reported in carcinoids. The diagnostic pitfalls of a pleomorphic carcinoid and the possible limitations of reaching this diagnosis on small biopsy specimens are discussed.