Primary gastrointestinal lymphoma in dogs occurs in the absence of peripheral lymphadenopathy, and the disease is often confined within the abdominal cavity. The intestines are the most frequently affected extranodal site.1 Dogs with gastrointestinal lymphoma often have protracted signs of gastrointestinal disturbance, including inappetence, weight loss, vomiting, or diarrhea, alone or in combination.2 Generally, the clinical signs are not distinguishable from other benign or malignant conditions, and consequently, the disease is often insidious in nature.
In contrast to multicentric (nodal) lymphoma, which is well studied in dogs, there is limited information in the veterinary literature characterizing primary gastrointestinal lymphoma in the absence of peripheral disease. Previous studies2–4 have evaluated clinicopathologic features and associated prognostic factors for dogs with lymphoma involving the gastrointestinal tract; however, the inclusion of dogs with multicentric lymphoma affecting the gastrointestinal tract limits the usefulness of those results. Nevertheless, previous small-scale studies3–7 had 2 similar observations. First, most dogs with primary gastrointestinal lymphoma had disease of the T-cell phenotype. Second, dogs with gastrointestinal lymphoma had a poor survival time, with many deaths attributable to the disease occurring within a few weeks to months after diagnosis. Identification of prognostic indicators has been limited to 1 study4 in which dogs that had diarrhea as a component of the disease had a poorer prognosis, with a shorter overall survival time, than dogs that did not.
Another confounder associated with earlier studies was the failure to distinguish among different anatomic locations in the gastrointestinal tract with the assumption that characteristics of the disease would not vary by location. Studies8,9 of human patients have found that certain histologic subtypes of lymphomas have a predilection to arise from specific sites in the gastrointestinal tract. Mucosa-associated lymphoid tissue lymphoma is typically found in the stomach, whereas diffuse large B-cell lymphoma is identified in various sites throughout the gastrointestinal tract.8,9 Enteropathy-associated T-cell lymphoma is a rare form of gastrointestinal lymphoma in people and is more commonly located in the jejunum than in other regions.9 Distinguishing among these histologic subtypes has proven useful in determining prognosis and treatment in human patients. To the authors' knowledge, this type of information has yet to be investigated in veterinary medicine. However, a recent report10 indicated that dogs with rectal lymphoma had an overall mean survival time of 1,697 days, raising the possibility that disease subtype and prognosis could vary by anatomic location in dogs with gastrointestinal lymphoma.
Chemotherapy is presently considered the mainstay of the treatment for gastrointestinal lymphoma in dogs, with most treatments relying on multiagent CHOP-based chemotherapy protocols. Rassnick et al4 evaluated the use of a CHOP-based chemotherapy protocol, VELCAP-SC, in 18 dogs with either primary gastrointestinal lymphoma or multicentric lymphoma affecting the gastrointestinal tract. In that study,4 10 of 18 dogs had remission, and the MST for all dogs was 77 days. Dogs that did not have remission had an MST of 10 days, and the median duration of remission for 9 dogs with complete remission was 86 days, suggesting that efficacy of a CHOP-based protocol for treatment of this disease is limited.
Much information is still needed to understand gastrointestinal lymphoma, and specifically primary intestinal lymphoma, in dogs. The purpose of the multi-institutional study reported here was to expand our limited knowledge of primary intestinal lymphoma in dogs by evaluating the signalment, clinicopathologic features, and outcomes of dogs with confirmed primary intestinal lymphoma and assessing factors potentially associated with survival times in these patients.
No outside funding or support was received in connection with this study. The authors declare that there were no conflicts of interest.
Presented in abstract form at the 28th Annual Conference of the Veterinary Cancer Society, Seattle, October 2008.
The authors thank Drs. Esther Chon, Brenda Phillips, Rebecca Seaman, and Pascale Salah for contributing cases.
Cyclophosphamide, doxorubicin, vincristine, and prednisone with or without l-asparaginase
Cyclophosphamide, vincristine, and prednisone
Mechlorethamine, vincristine, procarbazine, and prednisone
Median survival time
Mechlorethamine, vinblastine, procarbazine, and prednisone
Vincristine, l-asparaginase, cyclophosphamide, doxorubicin, and prednisone followed by 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, mechlorethamine, and procarbazine
CeeNU (lomustine) capsules, Bristol-Myers Squibb Co, Princeton, NJ.
Elspar, Merck & Co, Whitehouse Station, NJ.
Cyclophosphamide injection, BDI Pharma, Columbia, SC.
Adriamycin for injection, Bedford Laboratories, Bedford, Ohio.
Vincristine powder for injection, Advacare Pharma, Wilmington, Del.
Mustargen, Lundbeck Inc, Deerfield, Ill.
Vinblastine powder for injection, Advacare Pharma, Wilmington, Del.
Matulane, 50-mg tablet, Sigma-Tau Pharmaceuticals Inc, Gaithersburg, Md.
Dacarbazine, American Pharmaceutical Partners Inc, Schaumburg, Ill.
Melphalan tablets, ApoPharma Inc, Toronto, ON, Canada.
Leukeran tablets, GlaxoSmithKline, Research Triangle Park, NC.
Cytosar-U, Pharmacia & Upjohn, Simi Valley, Calif.
Cosmegen, Ovation Pharmaceuticals, Deerfield, Ill.
SPSS, version 20, IBM Corp, Armonk, NY.
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