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Description
Lymphoma is caused by malignant clonal expansion of lymphoid cells and most commonly arises from lymphoid tisses including the bone marrow, thymus, lymph nodes and spleen. Lymphoma is documented to be the most common haematopoietic neoplasm in dogs. In the dog, multicentric lymphoma is most common representing 80% of cases. Alimentary, cutaneous, mediastinal and extranodal sites are less common. Additionally the majority of lymphoma cases in dogs are of the B-cell immunophenotype.
In cats following the inroduction of widespread vaccination against FeLV testing and vaccination the most common type of lymphoma affecting cats is alimentary when previously it had been mediastinal and multicentric forms. Only 10% of lymphoma cases in cats is now associated with FeLV.
A staging system is used for lymphoma (Owen, 1980):
- Stage I - Involvement limited to a single node or lymphoid tissue in a single organ (excluding bone marrow)
- Stage II - Involvement of many lymph nodes in a regional area (+/- tonsils)
- Stage III - Generalised lymph node involvement
- Stage IV - Liver and/or spleen involvement (+ stage III)
- Stage V - Manifestations in the blood and involvement of bone marrow and/or other organ systems (+/-stages I-IV)
Each stage is then subclassifed as a) without systemic signs or b) with systemic signs.
Signalment
The median age of affected cats is 9-10 years and oriental breeds may be predisposed.
Affected dogs have a wide age range, most are middle-aged however young animals can be affected. There may also be a male predilection.
Diagnosis
Clinical Signs
Dogs: Multicentric Lymphoma
The most common presenting sign in dogs is a lymphadenopathy, with only 10-20% of dogs presenting clinically unwell. Dogs that do present with clinical signs may be anorexic, lethargic and have lost weight.
For other types of lymphoma affecting dogs the clinical signs will demonstrate the anatomical site affected.
Mediastinal forms will present with decreased heart sounds, dyspnoea and polyuria and polydypsia due to paraneoplastic hypercalcaemia. Dogs with mediastinal lymphoma can also have pitting oedema of the head and neck due to compression of the cranial vena cava.
Alimentary forms will present with vomiting, diarrhoea, anorexia and thickened loops on intestine on abdominal palpation.
Cutaneous lymphoma can also occur with a varied presentation but often present as cutaneous nodules.
Feline Lymphoma
In contrast to dogs, cats are more likely to present unwell. Again the clinical signs will depend on the anatomical location affected. Alimentary cats will present with vomiting, diarrhoea, weight loss and anorexia. 'Mediastinal cats will present with respiratory signs and may be in respiratory distress. Renal lymphoma also occurs in cats and affeted animals will present with signs similar to renal failure.
Physical Examination
An abdominal mass may be palpable and bowel loops may feel thickened in alimentary lymphoma. Additionally enlarged mesenteric lymph nodes and enlarged abdominal organs may be palpable . Muffled heart sounds and a non-compressible thoracic region may be found in mediastinal lymphoma. Petechiae, anaemia and icterus may also be present in any form of lymphoma.
Haematology and Biochemistry
Haematological analysis should always be performed with suspected lymphoma for staging purposes and for the recording of base-line parameters prior to the initiation of any treatment to assess the severity of any future myelosuppression. Potential abnormalities for those patients with bone marrow involvement may include lymphocytosis, thrombocytopenia, neutropenia and the presence of immature lymphoid precursors Affected cats are not usually leukemic. On biochemistry abnormalities may include hypoproteinaemia, elevated hepatic enzymes and elevated Blood Urea Nitrogen /creatinine.
FeLV/FIV
All cats with suspected lymphoma should be tested for FeLV and FIV, usually performed via enzyme-linked immunosorbent assay (ELISA) available in general practice in kit form (CITE test). Virus isolation would be required for a definitive result, however this is not only more time-consuming but is more expensive. An ELISA is also frequently used for the diagnosis of FIV.
Paraneoplastic Syndromes
Dogs may present with hypercalcaemia, this is due to the release of Parathyroid hormone- related protein (PTHrp) released by the tumor, which produces these effects by acting like parathyroid hormone. Affected cats are not usually hypercalcaemic
Radiography
A mass may be visible via plain or contrast abdominal radiography. Both abdominal and thoracic imaging is required in assessing the surrounding structures.
Ultrasonography
Superior to radiography in assessing infiltration or abnormalities of tissue architecture and assessing the surrounding structures for metastasis. Guided aspirates or biopsies may also be taken at this time, including lymph node sampling, to evaluate degree of systemic involvement.
Bone Marrow Aspirate/Biopsy
Should be taken ideally for all cases as part of the staging procedure.
Staging
Treatment
Surgery
Firstly, celiotomy is required for many cases of AL to obtain biopsy material. For solitary masses without systemic disease resection and anastomosis of the intestine is advised (single modality treatment). Local resection in cats has occasionally been curative. However, surgery alone may be insufficient for long-term control of the disease and if not all the tumour is able to be resected, or should relapse occur, or if there is systemic progression, chemotherapy will be required(multimodal treatment).
Radiotherapy
Lymphoma is highly radiosensitive and in theory should be efficient in treating all forms of lymphoma, however, surrounding tissues often have a low tolerance.
Chemotherapy
Combination chemotherapy is the most frequent method of treatment and the most commonly used protocols include:
- COP - Cyclophosphamide, Vincristine, Prednisolone. Frequently used in cats and can be used for induction therapy (8weeks) as well as a long term maintenance protocol
- COAP - Cyclophosphamide, Vincristine, Prednisolone, Cytosine arabinoside
- CHOP - Cyclophosphamide, Vincristine, Prednisolone, Doxorubicin, (potentiated sulphonamides)
Corticosteroids must not be administered prior to initiation of chemotherapy as they can cause resistance to cytotoxics and hence reduce the rate of response and the survival time. The aim is to induce remission and then continue with a maintenance regime, adjusting the dose as required with rescue therapy should relapse occur. Response to treatment can be monitored via reduction in tumour mass and size of lymph nodes. Haematological values should be frequently monitored to assess degree of effects of drugs. In particular animals should be moniores for the presence Azotaemia, neutropenia/sepsis, hypercalcaemia and pyrexia.
Supportive Therapy
Whilst receiving chemotherapy patients should recieve a high quality, palatable diet to maintain calorific intake. If animals become anorexic they should recieve appetite stimulation in cats e.g Cyproheptadine (Periactin) or antiemetics if vomiting occurs. Additionally fluid therapy, laxatives and analgesia may be required.
Prognosis
The mean survival times for dogs and cats without therapy is 6-8 weeks. For those recieving corticosteroids alone is 3 months. If chemotherapy is administered then the mean survival time increases to 6-9 months. Local canine lymphoma responds better to chemotherapy than the diffuse form of disease. Immunophenotype (T cell versus B cell lymphoma)does not appear to be associated with prognosis in cats as it can be in dogs. Factors indicating a better prognosis (overall survival) in cats include: an early presentation, a complete initial response to treatment and a clinically well patient(‘substage a’ disease).
In cats, response rate to induction chemotherapy is 26-79% and thus there is an apparently a poorer response rate in cats compared with dogs, however, 30-40% of cats that do have complete remission will maintain complete remission for two years or more and long-term maintenance chemotherapy can frequently be stopped and many will then live free of disease. Hence, dogs may have higher remission rates but are less likely than cats to be able to maintain remission without chemotherapy.
References
Hayes A. (2006) Feline lymphoma 1. Principles of diagnosis and management, In Practice, 28, pp 516-524
Head K. W, Else R. W, Dubielzig R.R, (2002) Tumours of the Alimentary Tract, in Tumours in Domestic Animals, 4th edition, Ed Menten D. J, Iowa State Press, Blackwell Publishing, Iowa, pp 471-472
Morris J, Dobson J (2001) Gastrointestinal Tract, in Small Animal Oncology, Blackwell Science, pp 228-239
Selting K. A, (2007), Intestinal Tumours, Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, fourth edition, Eds Withrow S.J, Vail D.M, Missouri, Saunders Elsevier, pp 491-501
White, R. A. S, (2003), Tumours of the intestines, in BSAVA Manual of Canine and Feline Oncology, second edition, Eds Dobson J. M, Lascelles B. D. X, Gloucester, British Small Animal Veterinary Association, pp 229-233