Gastrointestinal (GI) (or alimentary) lymphoma is the most common form of lymphoma in cats1-3. Feline GI lymphoma is histologically classified as low, intermediate or high grade according to the size and anaplasticity of the neoplastic lymphoid cells. Low-grade, small cell, lymphocytic feline GI lymphoma is composed of small relatively well-differentiated neoplastic lymphocytes, while high grade, lymphoblastic feline GI lymphoma is composed of large, poorly differentiated neoplastic lymphocyte. Clinical signs of low grade GI lymphoma are often chronic in nature, reflecting the generally slow onset and progression of the disease and commonly include weight loss, anorexia and lethargy with or without vomiting and diarrhea2-5. In contrast, high grade GI lymphoma is a more acute and severe disease3. Anorexia, weight loss, palpable abdominal mass and an acute presentation due to intestinal obstruction or perforation are common3. The epidemiology, presentation, diagnosis and staging of feline GI lymphoma are reviewed elsewhere2,3.

Important Considerations For Diagnosis Of GI Lymphoma

Definitive diagnosis of gastrointestinal lymphoma requires histological evaluation of gastrointestinal tissue. Although biopsy specimens can be obtained endoscopically or during exploratory laparotomy, recent evidence suggests full thickness gastrointestinal biopsies are superior to endoscopic biopsies in differentiating GI lymphoma from IBD, especially in the small intestine which is the most common site of feline GI lymphoma4. Further, histological evaluation of transmural intestinal biopsies along with extraintestinal tissue (mesenteric lymph nodes and liver) is helpful in differentiating neoplastic from inflammatory disease6.

Indications for surgery in cats with GI lymphoma are gastrointestinal obstruction, gastrointestinal perforation or to obtain biopsy samples of gastrointestinal and extraintestinal tissues (Richter). In most cases, chemotherapy is indicated following resection of a focal mass as microscopic diffuse intestinal involvement or systemic spread is likely2.

Chemotherapy For Low Grade GI Lymphoma

Prednisone or prednisolone (5-10 mg PO q24hrs) and chlorambucil (2 mg PO q2-3 days or 15mg/m2 PO q24 hours for 4 consecutive days, repeat every 3 weeks). The tendency for low grade lymphoma to be slowly progressive allows for outpatient treatment with a less intense, oral chemotherapy protocol5. Most cats with low grade GI lymphoma respond favourably to prednisone and chlorambucil therapy and experience extended survival times. Among 26 cats with low grade GI lymphoma treated with prednisone and chlorambucil, 9 demonstrated complete, 16 partial and 1 no response to treatment with a collective median survival time of 745 days5. In a separate study, 76% of cats (13/17) achieved complete remission with a median remission time of 18.9 months1. It has been demonstrated that cats that achieve complete remission achieve longer survival times than cats that do not1,5. However both groups of cats experience relatively long median survival times. Two recent retrospective reviews reported median survival times of 587 and 897 days for cats that achieved complete remission and 125 and 428 days for cats that did not1,5. The effect of chlorambucil regimen (alternate day versus high-dose pulse therapy) on median survival time has yet to be investigated. Adverse effects of chlorambucil therapy are infrequent and include gastrointestinal signs and myelosuppression (neutropenia and/or thrombocytopenia)1. A complete blood count (CBC) should be performed prior to initiation of therapy, one week after the first dose of chlorambucil and every 2-3 weeks (alternate day chlorambucil regimen) or prior to each chlorambucil treatment period (high dose pulse therapy chlorambucil regimen)3. Once complete remission is achieved and/or no leukopenia or trend towards leukopenia is observed on serial CBCs over a few months, the frequency of CBC monitoring can be decreased to once every 4-6 weeks3. Chlorambucil should be discontinued in cats with persistent or displaying a trend towards neutropenia or thrombocytopenia3. Cats with low grade lymphoma that do not respond to or develop progressive disease in the face of prednisone and chlorambucil therapy should be treated as per high grade lymphoma, described below.