Canine gastrointestinal lymphoma

Gastrointestinal lymphoma in the dog appears to be less com­mon than in the cat and much less has been published about it.^44-46 Gastrointestinal lymphoma accounts for approximately 5-20% of all canine lymphomas and is the most common extranodal form.^44-46 The majority of canine GI lymphomas are primary, with involvement in descending order of fre­quency of the small intestine, liver, regional lymph nodes, stomach, and colon.

1.5 to 14.7 years (means 6.7 and 7.7 years).^44,45 In one of these studies, 90% of dogs were male, while 48% were male in the other study.^44,45 Reported clinical signs in descending order of frequency were depression, vomiting, anorexia, diarrhea, weight loss, icterus, and tenesmus.⁴⁴ Vomiting and diarrhea of­ten occur together, and blood is visibly present in approxi­mately 50% of cases.⁴⁴ Generally, clinical signs are chronic and progressive, with acute exacerbations occasionally seen. The physical examination findings may include poor body condi­tion, the presence of an abdominal mass, abdominal pain, and hepatomegaly. Laboratory findings commonly reflect hepatic involvement when present, including increases in serum he­patic enzyme activities and serum bilirubin concentration. Other laboratory findings are usually nonspecific, with anemia and hypoalbuminemia being the most common abnormalities (each occurring in approximately 30% of dogs).⁴⁴ Plain ab­dominal radiographs may reveal hepatosplenomegaly and an abdominal mass if present.⁴⁴ Upper GI barium series may re­veal mucosal irregularities, luminal filling defects, and irregular wall thickening, suggesting infiltrative disease.⁴⁴ Ultrasonogra­phy may demonstrate an abdominal mass, gastric or intestinal wall thickening, ascites (suggesting peritonitis), and /or hepatic abnormalities.

Gross pathological findings are variable and are dependent on organ involvement. Most commonly, there are soft to firm cream-colored masses in the submucosa, which may extend into the lumen and transmurally into the serosa.⁴⁵ Some cases may also show diffuse disease. In one series of 15 cases, all the tumors originated from the submucosa, with most of the lesions consisting of diffuse infiltrates of non-cleaved cells.⁴⁴ In this case series, lymphoplasmacytic inflammation was com­mon both adjacent to as well as distant from the areas of lymphoma.⁴⁴ The junctional region between neoplastic and non-neoplastic tissue was not sharply demarcated, and often an inflamed mucosa was found to overlay a submucosal region of lymphoma.⁴⁴ Thus, there is a risk of missing the diagnosis of lymphoma and erroneously diagnosing IBD when biopsies are obtained endoscopically. In another study, epitheliotropism was common, with neoplastic lymphocytes infiltrating the superficial mucosal epithelium.⁴⁵ In this study, immunohisto­chemical staining determined that most canine GI lymphomas are primarily of T-cell origin.⁴⁵

Therapy for canine GI lymphoma is generally unrewarding. Since several segments of the GI tract are usually involved, surgical therapy alone is rarely effective as the sole treatment. As with other forms of lymphoma, a multi-agent chemother­apy protocol that incorporates doxorubicin is most effective, though only a small percentage of dogs with a GI lymphoma achieve a complete and/or durable remission with chemo­therapy.^44,46

Key Facts

■ Gastrointestinal lymphoma is a common cause of anorexia and weight loss in older cats, with or without vomiting and/or di­arrhea.

■ Most cats with GI lymphoma are FeLV and FIV negative.

■ Low-grade gastrointestinal lymphoma in cats may be more common than previously thought and appears to be more responsive to chemotherapy than high-grade lymphoma.

■ The most significant prognostic indicator for gastrointestinal lymphoma in cats is the initial response to chemotherapy, with patients that survive the initial induction period generally achieving long-term remission.

■ Gastrointestinal lymphoma in the dog may originate from the submucosa, which can make endoscopic diagnosis more difficult.

■ Gastrointestinal lymphoma in the dog often responds poorly or transiently to chemotherapy treatment.