Case 180525-1

12-year-old, female, spayed Boston terrier dog

This dog was presented for vomiting over a 9 month period. The increased frequency to at least once daily for previous 3 months. Otherwise the patient was bright, alert and responsive, and had good energy and appetite.

Abdominal ultrasound revealed thickened fundal rugae and the surrounding mesentery was hyperechoic. The lymph nodes in the area were enlarged. An endoscopy was performed, in which the duodenum had irregular blunted villi, and appeared edematous. The pylorus appeared normal. Fundal rugae appeared thickened and stiff. Pinch biopsies of the stomach and duodenum were submitted for biopsy.

This slide includes eleven pinch biopsies of stomach, including both fundus and pylorus, in which the architecture is disrupted by an unencapsulated, poorly demarcated, densely cellular mass consisting of disorganized cords, sheets, glands, and individualized neoplastic epithelial cells. In some sections these cells invade through the basement membrane and extend into the underlying lamina propria. These cells are often surrounded by dense streams of collagenous tissue (desmoplasia). Neoplastic cells polygonal, have variably distinct cell borders, and contain a moderate amount of finely granular to vesiculated eosinophilic cytoplasm. Cells often contain a clear cytoplasmic vacuole which peripheralizes the nucleus (signet ring cells). Nuclei are irregularly round, with coarsely stippled to vesiculated chromatin, and have one to two distinct nucleoli. Cells occasionally contain two to three nuclei. Anisocytosis and anisokaryosis are moderate, and there are 7 mitotic figures in ten 400X fields. In less affected regions, the lamina propria is infiltrated by small numbers of small lymphocytes and plasma cells. Within gastric glands of the fundic region, there are small numbers of spiral bacteria.

Immunohistochemistry with a pancytokeratin antibody revealed nvasive, disorganized and often individualized immunoreactive cells in multiple sections. Many contained a clear cytoplasmic vacuole, peripheralizing the nucleus (signet ring cells).

Stomach (fundus): Signet ring-cell carcinoma Stomach (fundus): Mild, diffuse, chronic lymphoplasmacytic gastritis with intraglandular spiral bacteria Stomach (pylorus): Moderate, diffuse, chronic lymphoplasmacytic gastritis with intraglandular spiral bacteria

The gastric samples had disorganized regions of gastric epithelium, which were associated with desmoplasia and in regions appeared to extend beyond the basement membrane. Many of the cells were signet ring cells. These findings were consistent with a signet-ring cell gastric carcinoma. There was also a mild, chronic gastritis within these sections.

The sections of duodenum examined (on a separate slide) had large numbers of small CD-3 positive lymphocytes within the mucosal epithelium, prompting suspicion for small T-cell lymphoma. Clonality showed a minor clonal population with polyclonal background, which was interpreted as an emergent small T-cell lymphoma in the context of the immunohistochemistry.

Conference attendees discussed the nomenclature of adenocarcinoma versus carcinoma in these cases. Traditionally, signet ring cell carcinoma is defined as a carcinoma because the characteristic signet ring cells do not form glandular structures. The diagnosis of signet ring cell carcinoma is based on more than 50% of the neoplastic population having the characteristic “signet ring” intra-cytoplasmic mucin. Other neoplastic cells within the mass can exhibit any number of features, including formation of glandular structures. The World Health Organization uses the term “adenocarcinoma” in the description of the signet ring cell carcinoma, and the delineation of terminology is not clear.

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