Neoplastic conditions of the stomach

Ann B. Hohenhaus

Introduction

Gastric tumors are rare in dogs. Typically, dogs with gastric tumors are older, with a median age of 10 years, but dogs less than 5 years old have also been reported.

Tumors can occur in any region of the canine stomach and there does not appear to be an anatomical predisposition for any particular region. One early case series found neoplastic tissue extending into both the body and pylorus of the stom­ach of most dogs with gastric tumors.⁷ More recently, the lesser curvature of the stomach has been a frequently described location for gastric tumors.^4,8,9 Carcinoma, leiomyoma, and leiomyosarcoma have been found to occur in the pyloric an- trum.²

Gastric tumors are exceedingly rare in cats. Lymphoma, which is a rare gastric tumor in the dog, is the most common gastric tumor in the cat. Three published case series including 96 cats with gastrointestinal tumors report a total of 3 cases of gastric carcinoma.^8,10,11 However, age, breed, and sex predilections cannot be determined from such a small number of cases.

Histology

Three major histological types of gastric tumors have been described: carcinomas, sarcomas, and round cell tumors, which are most commonly lymphoma. Although most gastric tumors in dogs are malignant, benign gastric tumors have also been reported.^2,9,12,13 Morphologically, carcinomas can be classified as intestinal (also called tubular) or diffuse (Table 4.7).⁵ The intestinal type of gastric carcinoma can be further differenti­ated into papillary, acinar, and solid.

Table 4.7: Histological types of gastric carcinoma

Subtype Form

Intestinal (tubular) type ■ Acinar

■ Papillary

■ Solid

Diffuse type ■ Adenocarcinoma

■ Undifferentiated carcinoma (signet ring)

Clinical signs

The clinical signs of gastric neoplasia are similar to those seen with other gastric disorders.Vomiting is common and in many cases is due to gastric outflow obstruction. Malignant ulcera­tion occurs in more than 50% of dogs with a gastric carcinoma (Figure 4.18). Hematemesis, melena, and pallor due to anemia are also commonly seen.^5,7 Tumor-associated nausea can be responsible for anorexia, weight loss, cachexia, and ptyalism.

Clinical pathology

The results of clinical pathology testing are not specific for gastric tumors in general or for a specific histological type of gastric neoplasia. Clinicopathological abnormalities are, in general, due to gastric inflammation, gastric outflow obstruc­tion, malabsorption, or blood loss. Hypoproteinemia and elevated liver enzymes are common.^1,3 In dogs with tumor- induced gastric outflow obstruction and vomiting, a hypo­chloremic metabolic alkalosis with paradoxical aciduria may develop.³ Frequently, a CBC demonstrates an inflammatory leukogram and anemia.^1,3 If the gastric bleeding is acute, the ensuing anemia will be regenerative, but if the hemorrhage is chronic, the anemia will become non-regenerative.

Diagnostic imaging

Diagnostic imaging is extremely important in determining the presence of a gastric mass and the extent of involvement of the surrounding organs. Unfortunately, the features of both benign and malignant gastric masses as well as the various histological types of gastric neoplasia overlap and neither ab­dominal radiography nor abdominal ultrasonography are use­ful in differentiating the specific tumor types.

Radiography

In some patients with gastric tumors, the survey radiographs may be normal. Abnormal findings include excessive fluid or gas in the stomach despite fasting.³ A mass or caudal displace­ment of the gastric axis on the lateral radiograph has been described in dogs with gastric tumors.²

The use of contrast agents facilitates the radiographic visuali­zation of gastric wall thickening, distortion of the gastric lu­men, presence of a filling defect, and derangement of the rugal folds caused by tumor infiltration. While the normal gastric emptying time is not well defined, delayed emptying is common with gastric tumors.^2,3 The stomach may also appear rigid and non-distensible, which is termed “linitis plastica” or “leather bottle stomach”. Ulcers can also be highlighted by contrast material.⁷

Ultrasonography

Both benign and malignant gastric tumors can be associated with mural thickening, loss of normal wall layering, and de­creased or absent motility in the area of the tumor.^1,3,12,16 The echogenicity of gastric tumors may be hypoechoic, hypere- choic, or mixed regardless of the histologic type.^12,16 Carcino­mas and lymphomas may appear as sessile masses or diffuse in distribution, while leiomyomas and leiomyosarcomas are typi­cally focal in distribution.¹² An ultrasound finding termed pseu­dolayering appears to correlate with an uneven intramural dis­tribution of tumor cells seen histologically in dogs with gastric carcinoma.¹ Extension of the tumor through the serosal surface of the stomach has been identified in dogs with carcinoma.¹²

The accuracy of ultrasonography increases with the expertise of the ultrasonographer.

Biopsy techniques

Although clinical signs, laboratory data, and diagnostic imag­ing may be suggestive of a gastric tumor, a biopsy is essential for a definitive diagnosis. Exploratory laparotomy can be used to obtain tissue samples for biopsy. Multiple samples can easily be obtained and are typically adequate in size for arriving at an accurate diagnosis, but the procedure is invasive. Gastro­scopy, using a fiberoptic or video endoscope, allows collection of a tissue sample and visualization of the gastric lesion prior

Figure 4.18:

Gastric adenocarcinoma in a dog. The arrows mark the outline of a gastric adeno­carcinoma. The entrance of the esophagus into the stomach is shown by the arrowheads.

to any therapeutic surgical procedure. Samples tend to be small and 10-20% of samples may be inadequate for obtaining an accurate diagnosis. Ultrasound-guided percutaneous fine needle aspiration of gastric masses to obtain cytologic samples has been reported; and this procedure appears to be useful for the diagnosis of gastric tumors in some patients.^1,3,17

Treatment

Because gastric tumors are rare and, in many cases, advanced at the time of diagnosis, reports of treatment are limited to single case reports. Surgery has been the primary treatment modality used in most cases. A relief of gastric outflow ob­struction by side-to-side gastrojejunostomy has been achieved.² Total gastrectomy or gastroduodenostomy have been at­tempted to achieve complete tumor resection.^2,18 One dog undergoing gastroduodenostomy was provided nutrition through a jejunostomy tube and was also treated with chemo­therapy using a combination of cisplatin, 5-fluorouracil, doxo­rubicin, and cyclophosphamide.² Photodynamic therapy has also been reported for the treatment of a gastric carcinoma in a single case.⁴

Systemic complications of gastric neoplasia

Hypochloremic metabolic alkalosis resulting in paradoxical aciduria occurs in dogs with gastric carcinoma and severe vomiting.³ Vomiting leads to the loss of hydrogen and chloride

Figure 4.19:

Gastric perforation in a dog with gastric adenocarcinoma.

ions, alkalosis, and volume depletion. Normally, the renal tu­bules will resorb sodium ions in exchange for chloride ions in response to alkalosis and hypovolemia. However, when chlo­ride is depleted, the kidneys resorb sodium and excrete hydro­gen ions instead of chloride in order to maintain electrical neutrality, leading to a paradoxical aciduria.

Iron deficiency anemia results when gastric tumors cause ul­ceration and chronic GI blood loss. Loss of iron into the feces and inadequate intake of replacement iron due to vomiting and anorexia result in a microcytic, hypochromic, non-regen- erative anemia.

Paraneoplastic hypoglycemia with a low serum insulin con­centration has been described in a dog with a gastric leiomy- osarcoma.¹⁹ The diagnostic investigation of this patient sug­gested the synthesis of an unidentified hypoglycemic factor by the tumor. Non-islet cell tumors associated with hypo­glycemia such as this one are typically large and palpable on physical examination.¹⁹ Pneumoperitoneum results when the tumor erodes through the entire gastric wall (Figure 4.19).²0

Tumor invasion and metastasis

All histological types of gastric tumors are highly metastatic. Gastric carcinomas most commonly metastasize to the re­gional lymph nodes, but they can also widely disseminate to other abdominal organs, the central nervous system, the myo­cardium, mediastinum, long bones, and testicular connective tissue.^2,4,16,21,22 The single case of a gastric carcinoid tumor in a cat was found to have metastasized to the kidney, brain, liver, spleen, lung, and lymph node.¹¹ Gastric leiomyosarcomas have been shown to metastasize to the liver and duodenum ².

Survival

In general, the survival of dogs with gastric cancer is poor. One case series reported a median survival time of 3 days with a range of 0 days to 10 months.² Occasionally, longer survival times have been reported in single cases.

??Θ Key Facts

■ Most gastric tumors are malignant and are highly metastatic.

■ Diagnostic imaging, plain radiography, contrast radiography, and ultrasonography contribute to the diagnosis of gastric tumors; however, a biopsy is required to make a definitive diagnosis and to determine if the tumor is benign or malignant.

■ Tissue samples can be obtained via exploratory laparotomy or endoscopy.

■ Between 10-20% of the time, a sample obtained via endoscopy will be inadequate to diagnose gastric cancer.

■ In general, survival in dogs and cats with gastric neoplasia is poor due to the advanced stage of disease at the time of diagnosis.

References

1. Penninck DG, Moore AS, Gliatto J. Ultrasonography of canine gastric epithelial neoplasia. Vet Radiol Ultrasound 1998; 39: 342— 348.

2. Swann HM, Holt DE. Canine gastric adenocarcinoma and leiomy­osarcoma: a retrospective study of 21 cases (1986—1999) and litera­ture review.JAm Anim Hosp Assoc 2002; 38: 157—164.

3. Rivers BJ, Walter PA, Johnston GR et al. Canine gastric neoplasia: utility of ultrasonography in diagnosis. J Am Anim Hosp Assoc 1997; 33:144-155.

4. Fonda D, Gualtieri M, Scanziani E. Gastric carcinoma in the dog: a Hinicopathological study of 11 cases. JAm Small Anim Prac 1989; 30: 353-360.

5. Patnaik AK, Hurvitz AI, Johnson GF. Canine gastric adenocarci­noma. Vet Pathol 1978; 15: 600-607.

6. Sullivan M, Lee R, Fisher EW et al. A study of 31 cases of gastric carcinoma in dogs. Vet Rec 1987; 120: 79-83.

17. Sautter JH, Hanlon GF. Gastric neoplasms in the dog: a report of 20 cases. JAm Vet Med Assoc 1975; 166: 691-696.

18. Gualtieri M, Monzeglio MG, Scanziani E. Gastric neoplasia. Vet Clin North Am 1999; 29: 415-440.

9. Easton S. A retrospective study into the effects of operator experi­ence on the accuracy of ultrasound in the diagnosis of gastric neo­plasia in dogs. Vet Radiol Ultrasound 2001; 42: 47-50.

10. Brodey RS. Alimentary tract neoplasms in the cat: a clinicopatho- logic survey of 46 cases. Am J Vet Res 1966; 27: 74-80.

11. Turk MAM, Gallina AM, Russell TS. Nonhematopoietic gastroin­testinal neoplasia in cats: a retrospective study of 44 cases. Vet Pathol 1981; 18: 614-620.

12. Lamb CR, Grierson J. Ultrasonographic appearance of primary gas­tric neoplasia in 21 dogs. J Small Anim Prac 1999; 40: 211-215.

13. Kapatkin AS, Mullen HS, Matthiesen DT et al. Leiomyosarcoma in dogs: 44 cases (1983-1988). J Am Vet Med Assoc 1992; 201: 1077­1079.

14. Albers TM, Alroy J, McDonnell JJ. A poorly differentiated gastric carcinoid in a dog.J Vet Diagn Invest 1998; 10: 116-118.

15. Rossmeisl JH, Forrester SD, Tobertson JL et al. Chronic vomiting associated with a gastric carcinoid in a cat. J Am Anim Hosp Assoc 2002; 38: 61-66.

16. Kaser-Hotz B, Hauser B, Arnold P. Ultrasonographic findings in ca­nine gastric neoplasia in 13 patients. Vet Radiol Ultrasound 1996; 37: 51-56.

17. Crystal MA, Penninck DG, Matz ME et al. Use of ultrasound-guided fine-needle aspiration biopsy and automated core biopsy for the diagnosis of gastrointestinal diseases in small animals. Vet Radiol Ul­trasound 1993; 34: 438-444.

18. Sellon RK, Bissonnette K, Bunch SE. Long-term survival after total gastrectomy for gastric adenocarcinoma in a dog. J Vet Intern Med 1996; 10: 333-335.

19. Bellah JR, Ginn PE. Gastric leiomyosarcoma associated with hy­poglycemia in a dog. JAm Anim Hosp Assoc 1996; 32: 283-286.

20. Mellanby RJ, Baines EA, Herrtage ME. Spontaneous pneumoperi­toneum in two cats. J Small Anim Pract 2002; 43: 543-546.

21. Esplin DG, Wilson SR. Gastrointestinal adenocarcinomas metastatic to the testes and associated structures in three dogs.J Am Anim Hosp Assoc 1998; 34: 287-290.

22. Wang FI, Lee JJ, Liu CH et al. Scirrhous gastric carcinoma with mediastinal invasion in a dog.J Vet Diagn Invest 2002; 14: 65-68.

23. Beck C, Slocombe RF, O’Neill T et al. The use of ultrasound in the investigation of gastric carcinoma in a dog. Aust Vet J 2001; 79: 332­334.

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