Lymphomas are irregular (neoplastic) growth of lymphoid tissue as tumors, which can affect a single organ (e.g. kidney, mesenteric or mediastinal lymph node, spleen or liver). Whereas lymphoma have been classically defined as neoplastic cells found in fluid exudates (such as ascitic fluid), lymphosarcoma usually refers to solid tumours within organs, but such classification is academic and from a clinical perspective. However, since treatment regimens are pragmatically identical, we have adopted the generic term lymphoma to refer to any neoplastic change of lymphocytes that does not involve leukemia.
Lymphomas may occur within a lymph node (nodal) or outside lymph node tissue (extra-nodal) and are classified as either B-cell lymphoma or T-cell lymphoma. Regardless of classification, feline lymphoma invariably receive the same veterinary treatment.
Feline lymphomas differ from canine lymphomas. Most canine lymphomas are composed of large lymphocytes, with only a low incidence of well-differentiated small cell lymphomas. Feline lymphoma is most often an intermediate or large cell type, but small cell lymphomas are much more common in cats than in dogs. Small cell lymphomas are often seen in older cats, most commonly in the alimentary tract or liver, whereas large cell lymphomas are seen more frequently in younger cats (<6 years of age). Feline lymphoma is often more challenging to diagnose than canine lymphoma because small cell lymphomas are difficult to differentiate cytologically from a lymphoid inflammatory infiltrate or reactive hyperplasia. Definitive diagnosis of small cell lymphoma often requires histopathology, and the practicing cytologist must be aware of the cytologic appearance of feline lymphoma to accurately interpret cytologic findings and determine the necessity of surgical biopsy.
Classifications of feline lymphoma
The classifications of feline lymphoma are loosely based on anatomical site involvement.
- Multicentric lymphoma - generally involves multiple lymph nodes and possibly multiple organs. This form is more closely associated with feline leukemia and the prognosis for this form is not as good, especially if the cat is feline leukemia positive.
- Mesenteric lymphoma - very common in cats over 10 years of age. The intestinal form affects the small intestine but sometimes the stomach, leading to gastric lymphoma. This form is least likely to be associated with feline leukemia.
- Renal lymphoma - most common neoplasia of the feline kidney, primarily affecting older cats
- Hepatic lymphoma - primary hepatic lymphoma is relatively common
- CNS lymphoma - rare and often associated with renal lymphoma or multicentric lymphoma.
- Neurolymphomatosis - rare form of primary lymphoma associated with chronic, progressive polyneuropathy.
- Low-grade alimentary lymphoma (LGAL) - aged cats, usually confined to intestinal lumen. Clinically indistinguishable from lymphocytic-plasmacytic irritable bowel disease
- Cutaneous lymphoma
- Thymic/mediastinal lymphoma - also associated with feline leukemia, and limited to the thoracic cavity (thymus gland and associated lymph nodes).
- Polyostotic lymphoma - involves multicentric bone involvement and lymphadenopathy
- Inflammatory processes - no definitive proof exists as yet to conclude that chronic inflammation leads to formation of feline lymphoma, but inflammation-associated neoplasia is well-established. An association between chronic inflammatory bowel disease and development of feline T-cell lymphoma has been suggested. Concurrent lymphocytic-plasmacytic IBD has been identified in other regions of the alimentary tract in up to 20% of cats with LGAL.
- Environmental - a variety of chemicals such as aromatic benzenes, organophosphates and dioxins (DDT and 2,4,5-T) are implicated in human lymphoma, and cannot be excluded as possible causes of feline lymphoma.
- Nutritional - the proven relationship between nutrition and neoplasia in humans suggests a plausible link between nutrition and lymphoma in cats, although more work is needed in this area.
- Bacterial - Spirochetes have been observed in a feline epitheliotropic T- cell gastrointestinal tract lymphoma and a natural killer-like T cell lymphoma. There were Helicobacter spp-like organisms and Spirochetes in a cougar affected with gastroduodenal adenocarcinoma and rectal adenoma. Unlike in human lymphomas associated with Helicobacter pylori or Borrelia burgdorferi, the etiologic significance of spiral-shaped bacteria is not clear in feline lymphoid neoplasms. Records of bacteria belonging to the genus Helicobacter, such as Flexispira suggests a possible synergistic role of bacteria in the etiopathogenesis of feline lymphoma.
- Genetic - breed predisposition (e.g. Maine coon) and familial susceptibility have been implicated anecdotally but no evidence to prove such hypotheses has surfaced.
- - in some cases, FeLV-associated lymphoma follows infection with the feline leukemia virus (FeLV). FeLV has a strong association with development of mediastinal and muticentric lymphoma in cats (60 fold increased risk).
- - FIV also increases the risk of lymphoma formation in cats, but less so, compared with FeLV (5 fold increased risk). An indirect role is favoured for FIV in the development of extranodal B-cell neoplasms in cats. Possible effects of the FIV infection that can lead to lymphosarcoma include activation of ß lymphocytes with the eventual emergence of malignant cells from the proliferating ß-cell pool, chronic dysregulation of the immune system, or activation of oncogene pathways that facilitate the malignant transformation of normal cells.
The most common clinical signs are weight loss, inappetence, vomiting and/ or diarrhea, lethargy, and polyphagia. Vomiting and/or diarrhea are considered common signs and 20% of all cats biopsied with chronic intermittent vomiting and diarrhoea have been shown to caused by diffuse intestinal lymphoma. Abdominal palpation is usually abnormal, with nodules and tumors often palpable in mesenteric lymph nodes. Regional lymph nodes may also be involved, including mandibular, popliteal and superficial cervical (prescapular) nodes. The most common ultrasonographic finding are increased intestinal wall thickness with preservation of layering.
Feline lymphoma has several different forms. In all forms, the tumors consist of abnormal proliferations of lymphoid tissue. Because lymphocytes and lymph tissue are found throughout the body, lymphoma can appear almost anywhere and affect a wide number of organs. Lymphoma more commonly appears, though, in three parts of the body. The location is often associated with the cause of the lymphoma and influences the clinical signs, treatment, and prognosis.
In all forms, the treatment outcome is more guarded if the cat is positive for Feline leukemia virus (FeLV).
Diagnosis of lymphoma in cats is based on a series of observations and tests. A physical exam may revealing swellings in the lymph nodes or GI tract. Radiographs, ultrasounds or physical examinations may show tumors or swellings in other internal organs.Testing for FeLV and FIV may reveal that a cat is positive for one of these diseases, which increases the likelihood that she could develop feline lymphoma. A chemistry panel and complete blood count (CBC) may reveal particular organ involvement or an anemia, particularly in the multicentric form or in the FeLV positive cat. Fine needle aspirate or biopsies are often diagnostic for feline lymphoma. When a trained pathologist examines a fine needle aspirate or a biopsy, he or she is looking for a uniform population of immature lymphoid cells, which confirms feline lymphoma.
Hematological changes include mild anaemia, monocytosis and/or neutrophilic leucocytosis (Lingard, et al, 2009). Hypoalbuminaemia appears to be a relatively constant sign, depending primarily on the grade of lymphoma, with high-grade cases showing greater extents of hypoalbuminaemia.
Other causes of gastrointestinal disease with signs of vomiting, weight loss and/or diarrhoea include irritable bowel disease, gastritis, FIP, bacterial gastroenteritis, parasites, and obstructive causes (e.g. pyloric stenosis, foreign body, Intussusception, intestinal polyps, Feline gastrointestinal eosinophilic sclerosing fibroplasia).
Differential diagnoses of non-lymphoma neoplasia associated with lymphoid tissues include Feline Hodgkin's-like disease, B-cell lymphoma, Follicular lymphoma, and DPLH - distinctive peripheral lymph node hyperplasia
Table. 1. Histological classification of lymphoproliferative diseases in cats
|Low grade||Chronic lymphocytic leukemia||CLL|
|Small lymphocytic lymphoma||SLL|
|Small lymphocytic intermediate lymphoma||SLLI|
|Small lymphocytic plasmacytoid/plasmacytoma||SLLP|
|Follicular small cleaved-cell lymphoma||FSC|
|Follicular mixed-cell lymphoma||FM|
|Intermediate grade||Follicular large-cell lymphoma||FL|
|Small cleaved-cell lymphoma||SCC|
|Large cleaved-cell lymphoma||LCC|
|High grade||Acute lymphocytic leukemia||ALL|
|Immunoblastic small-cell lymphoma||IBS|
|Immunoblastic polymorphous lymphoma||IBP|
|Small noncleaved-cell lymphoma||SNC|
|Lymphoblastic convoluted-cell lymphoma||LBC|
The remission and survival rates of cats with lymphoma vary depending on the cat's FeLV status, the location of the tumor(s) and how quickly the tumor is diagnosed and treated. In general, about 70% of cats will respond to the chemotherapy treatment. On average, these cats will live an additional 4 to 16 months. However, about 30% - 40% of the cats that respond will go into a more complete remission that can last for 2 years or longer. This potential response is encouraging and is the reason that treatment for lymphoma in cats is so highly recommended. Cats that are not treated have an average survival time of only 4 to 6 weeks once the diagnosis has been made. Cats that are infected with FeLV or FIV have a lower rate of response to therapy as well as a shorter average survival time when treated.
Table 2. The University of Pennsylvania feline weekly sequential lymphoma protocol (2009)
|Treatment week||Drug, dosage and route|
|1||L-asparaginase (Leunase) 400 IU/kg SQ weekly|
|2||Chlorambucil (Leukeran) 0.5 mg/m2, IV|
|3||Cyclophosphamide 50mg PO (25mg PO day 1 and 25mg PO on day 3)|
|4||Vincristine 0.5mg/m2, IV|
|5||Methotrexate 2.5 mg PO|
|6-9||Repeat week 2-5|
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