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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Gastric neoplasia of horses is rare; SCC, adenocarcinoma, lymphoma, leiomyosarcoma, and leiomyoma account for 1.5% of all equine neoplasms
  • SCC usually originates in the squamous portion of the stomach, infiltrates the wall, and projects into the lumen. There are 2 types of SCC: erosive and productive/proliferative. Both types may be present simultaneously
  • Although SCC is the most common gastric neoplasm, only 3% of carcinomas in horses are of gastric origin
  • SCC lesions of the stomach may reach a considerable size owing to local invasiveness and have a proliferative appearance. They are often ulcerated and secondarily infected. The surface may then have a grayish-white and hemorrhagic appearance. There may be adhesions of the stomach to adjacent liver, spleen, or diaphragm, and there are frequently metastatic nodules in the abdominal and thoracic cavities; however, this metastatic form progresses slowly. The tumors may cause physical obstruction in the stomach and may occasionally be associated with severe intraluminal hemorrhage
  • Adenocarcinoma of the glandular part is very rare in horses and it may affect the pylorus and the fundic region. Although adenocarcinomas may project into the gut lumen, the predominant feature is growth from the mucosa into the submucosa and the muscularis to the serosa
  • Leiomyosarcoma affects the cranial aspects of the stomach
  • Other signs may be related to the effects of metastases (e.g. pleural effusion)

Signalment!!navigator!!

  • Horses of middle age and older (range 8.6–14.6 years with an increased risk between 11 and 12 years) are susceptible to SCC, and a 4:1 male to female ratio has been reported
  • Breeds with an increased risk of developing SCC are draft horses, Appaloosas, American Paints, Pintos, and mixed breeds
  • Adenocarcinoma and lymphoma have a similar age distribution

Signs!!navigator!!

  • Clinical signs are usually vague and rarely lead to the stomach as the affected organ
  • Affected horses have a history of gradual weight loss, anorexia, halitosis, dysphagia, ptyalism, and lethargy extending over 2–6 weeks
  • Abdominal pain and difficulty in eating or swallowing are not usually features of gastric neoplasia
  • Pallor of mucous membranes and an increase in heart rate may be seen due to anemia resulting from gastric hemorrhage or depressed erythrogenesis
  • Recurrent episodic pyrexia up to 40°C may occur as the result of necrosis in the neoplasm, and the respiratory rate may be raised in response to metastatic masses or pleural effusion in the thorax
  • Ascites and ventral edema may be primary signs in a few horses, so that despite the weight loss the abdomen appears distended
  • Fecal consistency is variable

Causes and Risk Factors!!navigator!!

None determined, but dietary excesses, mineral and vitamin deficiencies, and chronic irritation have been suggested such risk factors.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

A definitive diagnosis is made on histologic examination of tissue obtained by endoscopic biopsy or at autopsy.

Differential Diagnosis!!navigator!!

See chapter Chronic weight loss.

CBC/Biochemistry/Urinalysis!!navigator!!

The packed cell volume may be low at 12–28% with gastric carcinoma.

Other Laboratory Tests!!navigator!!

  • Feces may test positive for occult blood
  • Neoplastic cells may be found in fluid recovered by gastric lavage, in peritoneal fluid, or in pleural fluid

Imaging!!navigator!!

  • Endoscopy using a video or fiber endoscope of 2 m in length or more enables direct visualization and biopsy of the gastric growth in adult horses
  • Exploratory laparotomy or standing laparoscopy allows an examination of the serosal surface of the stomach, determines the extent of the spread of the tumor if any, and allows biopsy of the primary mass or metastatic nodules
  • Radiographs of the thorax may reveal pleural effusion. A pneumogastrogram may be of value in delineating the intraluminal portion of the tumor
  • Ultrasonography from the left cranial abdomen may show thickening and abnormal echogenicity of the stomach wall

Other Diagnostic Procedures!!navigator!!

Rectal examination may indicate metastatic masses or increased abdominal fluid. Abdominocentesis is normal when the tumor is confined in the stomach but may be an exudate if it has spread.

Treatment ⬆ ⬇

TREATMENT

By the time a diagnosis is made the tumors have usually progressed beyond the point where any treatment is feasible, and euthanasia is the only option. No report of successful therapy was found.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

N/A

Contraindications/Possible Interactions!!navigator!!

N/A

Follow-up ⬆ ⬇

FOLLOW-UP

N/A

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Abbreviations!!navigator!!

SCC = squamous cell carcinoma

Suggested Reading ⬆ ⬇

East LM, Savage CJ. Abdominal neoplasia (excluding urogenital tract). Vet Clin North Am Equine Pract 1998;14;475–493.

Head KW, Else RW, Dubielzig RR. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in Domestic Animals, 4e. Ames, IA: Iowa State Press, 2002:401–481.

Knottembelt DC, Patterson-Kane JC, Snalune JC. Clinical Equine Oncology. Edinburgh, UK: Elsevier, 2015:429–479.

Author(s) ⬆

Author: Olimpo Oliver-Espinosa

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa