The tumour is composed of round and irregular-shaped neoplastic epithelial cell nests or clusters floating in mucus-filled cystic cavities separated by connective fibrous strands. The tumour cells are cuboidal, columnar or irregular in shape, usually possess clear cytoplasm and darkly-stained, centrically placed nuclei. The tumour cells may have atypical nuclei, but mitotic figures are sparse. The tumour cells are arranged in solid clusters and tend to form secondary lumens or incomplete duct-like structures. Mucus-producing cells may arrange in a papillary pattern projecting into the mucous pools. Mucous acinus-like tumour islands may also be present. Both intracellular and extracellular mucin components show positive staining for periodic acid Schiff, Alcian blue and mucicarmine.
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