B

Fig. 3.12 A Papillary adenocarcinoma. B Well differentiated mucinous adenocarcinoma.

nomas is unreliable in tumours containing only a few cells. The term 'mucin-produ-cing' is not synonymous with mucinous in this context.

Signet-ring cell carcinomas

More than 50% of the tumour consists of isolated or small groups of malignant cells containing intracytoplasmic mucin.

Superficially cells lie scattered in the lamina propria, widening the distances between the pits and glands. The tumour cells have five morphologies: (1) Nuclei push against cell membranes creating a classical signet ring cell appearance due to an expanded, globoid, optically clear cytoplasm. These contain acid mucin and stain with Alcian blue at pH 2.5; (2)

other diffuse carcinomas contain cells with central nuclei resembling histiocytes, and show little or no mitotic activity; (3) small, deeply eosinophilic cells with prominent, but minute, cytoplasmic granules containing neutral mucin; (4) small cells with little or no mucin, and (5) anaplastic cells with little or no mucin. These cell types intermingle with one another and constitute varying tumour proportions. Signet-ring cell tumours may also form lacy or delicate trabecular glandular patterns and they may display a zonal or solid arrangement. Signet-ring cell carcinomas are infiltrative; the number of malignant cells is comparatively small and desmoplasia may be prominent. Special stains, including mucin stains (PAS, muci-carmine, or Alcian blue) or immunohisto-chemical staining with antibodies to cytokeratin, help detect sparsely dispersed tumour cells in the stroma. Cyto-keratin immunostains detect a greater percentage of neoplastic cells than do mucin stains. Several conditions mimic signet-ring cell carcinoma including signet-ring lymphoma, lamina propria muciphages, xanthomas and detached or dying cells associated with gastritis.

Lauren classification

The Lauren classification {1021} has proven useful in evaluating the natural history of gastric carcinoma, especially with regard to its association with environmental factors, incidence trends and its precursors. Lesions are classified into one of two major types: intestinal or diffuse. Tumours that contain approximately equal quantities of intestinal and diffuse components are called mixed carcinomas. Carcinomas too undifferentiated to fit neatly into either category are placed in the indeterminate category.

Intestinal carcinomas

These form recognizable glands that range from well differentiated to moderately differentiated tumours, sometimes with poorly differentiated tumour at the advancing margin. They typically arise on a background of intestinal metaplasia. The mucinous phenotype of these cancers is intestinal, gastric and gastrointestinal.

Diffuse carcinomas

They consist of poorly cohesive cells diffusely infiltrating the gastric wall with little

¿it VJ* /; éf C

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