ACs are infiltrative tumours that grow in a variety of patterns, including small nests, sheets, trabeculae, glands and/or a combination of these patterns. Cysts with intracystic papillary-like projections of tumour cells may also be seen. In contrast to TCs, the cells are larger and the nuclei are often vesicular and contain prominent nucleoli. Mitoses (usually 210/10 HPFs) necrosis, cellular pleomor-phism and angiolymphatic invasion are common. Some tumours may even fulfill the diagnostic criteria of large cell neuroendocrine carcinoma of the lung (10 or more mitoses per 10 high power fields and prominent necrosis). Mucinous changes, amyloid, spindle cells and oncocytic-oncocytoid cells may also be observed.


The tumours may stain for synaptophysin (100%), cytokeratin (96%), chromogranin A (94%), calcitonin (80%), CEA (75%), somatostatin (50%), serotonin (21%), and adrenocorticotrophic hormone (17%) {2816}.

Electron microscopy

Membrane-bound, electron-dense neu-rosecretory granules ranging from 70420 nm are prominent {2769}. Cellular junctional complexes, rough endoplas-mic reticulum, mitochondria, Golgi complexes and infrequent bundles of tonofil-aments may also be seen.

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