Histopathology

Shared by all tumours in this group are the presence of glandular or duct-like structures, infiltrative growth into parenchyma or surrounding tissues, and lack of features that characterize other salivary adenocarcinomas. There is considerable variability in the architectural structure. Some have small confluent nests or cords of tumour cells, others large discrete islands with intervening trabeculae of fibrous connective tissue, and still others large solid, densely cellular sheets. This latter group reveals very limited stromal connective tissue. Ductal differentiation is widespread in low and intermediate grade tumours but usually much more subtle in high-grade tumours. Small cysts are occasionally present in those with numerous ducts. Cuboidal or ovoid cells predominate in most tumours but scattered clear and oncocytic cells are occasionally evident. Small deposits of eosinophilic acellular material and extracellular mucin may be present.

Unlike most other salivary adenocarcinomas, the cytologic variability is useful for grading these tumours {2447}. Low-grade

Fig. 5.27 Adenocarcinoma, not otherwise specified.. A Architectural and cellular variability. Prominent ductal differentiation is present, within closely arranged tumour islands. B Focal tubular structures with hyaline cores, reminiscent of adenoid cystic carcinoma.

Fig. 5.28 Adenocarcinoma, not otherwise specified. A This example demonstrates an organoid arrangement of cells that have abundant eosinophilic and clear cytoplasm. B Low-grade tumours are characterized by distinct ductal differentiation, cells with limited nuclear variability and uniform nuclei that have small nucleoli, and rare mitoses. C Intermediate grade. Greater variability in the size, shape and staining of the nuclei is typically present. Nucleoli are often more prominent and scattered mitoses are often present. D Large, hyperchromatic, pleomorphic nuclei and frequent mitoses characterize high-grade tumours. Although ductal differentiation is present in these infiltrating tumour islands, other areas had large solid sheets of similar cells with rare to no ductal differentiation.

Fig. 5.28 Adenocarcinoma, not otherwise specified. A This example demonstrates an organoid arrangement of cells that have abundant eosinophilic and clear cytoplasm. B Low-grade tumours are characterized by distinct ductal differentiation, cells with limited nuclear variability and uniform nuclei that have small nucleoli, and rare mitoses. C Intermediate grade. Greater variability in the size, shape and staining of the nuclei is typically present. Nucleoli are often more prominent and scattered mitoses are often present. D Large, hyperchromatic, pleomorphic nuclei and frequent mitoses characterize high-grade tumours. Although ductal differentiation is present in these infiltrating tumour islands, other areas had large solid sheets of similar cells with rare to no ductal differentiation.

tumours demonstrate minimal variability of nuclear size, shape, or staining density, and rare mitoses. In some, the bland nuclear morphology suggests benignity and determination of their malignant nature is based largely on the identification of invasive growth. Intermediate grade tumours show nuclear variability and more frequent mitoses. High-grade tumours have enlarged, pleomorphic, hyperchro-matic nuclei, focal necrosis, and frequent and atypical mitoses. The presence of ductal differentiation helps in the distinction from undifferentiated carcinoma.

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