Malignant transformation and subsequent leptomeningeal carcinomatosis of a gastric polyp in a dog

Dillon S. Didehvar, Matthew R. Lanza, Matthew J. Atherton, Jennifer A. Lenz

Background

This study presents a unique case of progressive carcinogenesis from a gastric polyp to gastric adenocarcinoma, culminating in leptomeningeal carcinomatosis in an adult male Scottish terrier. Such transformation and progression in dogs have not been previously documented in veterinary oncology, making this case significant for understanding gastric carcinoma in dogs as a model for human disease. Gastric carcinoma is a severe disease with poor prognosis and high metastatic potential, emphasizing the need for better understanding of its pathogenesis in both humans and canine models.

Methods

The progression of the disease was documented over 14 months through repeated clinical evaluations and surgical biopsies. Initially, the dog presented with vomiting and hematemesis. Diagnostic procedures included blood tests, ultrasound examinations, and endoscopy. Over time, biopsies confirmed the progression from a benign gastric polyp to invasive gastric adenocarcinoma. The treatment included surgical removals of the polyp and later, the carcinoma, along with adjuvant chemotherapy using carboplatin and 5-fluorouracil, followed by toceranib phosphate after presumed metastasis was detected.

Results

Initially, the dog had a gastric polyp, which was surgically removed and diagnosed as benign. Within a year, a new gastric mass developed at the same site, which upon removal and histopathological examination, was diagnosed as gastric adenocarcinoma. Postoperative evaluations showed no immediate evidence of metastasis. However, recurrence and metastasis were later confirmed, with metastatic lesions found in abdominal lymph nodes and the peritoneum. Eventually, leptomeningeal carcinomatosis was diagnosed, characterized by the presence of carcinoma cells across the central nervous system's meninges, an uncommon terminal event.

Limitations

The study is a single case report, which limits the generalizability of the findings. However, it provides valuable insights into the potential malignant transformation of gastric polyps in dogs, an area that has not been widely recognized or studied previously.

Conclusions

This case highlights the potential for malignant transformation of gastric polyps in dogs, which parallels the known risk in humans. The findings suggest that gastric polyps in dogs might not be as benign as previously considered and could have implications for veterinary practices regarding the monitoring and treatment of gastric polyps. This case also emphasizes the importance of canine models in understanding gastric carcinogenesis relevant to human medical research. Future studies should focus on the characterization and treatment implications of gastric polyps in dogs to better manage and understand this disease.

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