Lymphomas in dogs: predictors of long-term survival

Epidemiology and risk factors

Lymphomas in dogs represent around 5–7% of all neoplasms and about 80% of haematopoietic tumours, which are related to tissues that produce blood cells.

Lymphoma usually affects adult dogs around 5–11 years old and there is a degree of predisposition in certain breeds, for example Boxer, Basset Hound, St. Bernard, German Shepherd, Golden Retriever, etc.

Although the underlying causes remain unknown, apart from genetics, some risk factors are thought to play a role, both environmental (exposure to herbicides, chemicals, tobacco smoke) and exposure to certain viruses or even immune-mediated causes (use of cyclosporine or other immunosuppressive drugs).

Lymphomas in dogs: classification

Lymphomas in dogs can be classified according to different criteria, such as the anatomical location, histology, or the immunophenotype or molecular characteristics.

Classifying a lymphoma is a complicated yet very important task with regard to its treatment and prognosis.

Lymphomas are classified as follows, depending on their location:

• Multicentric: This is the most common form in dogs. It presents as generalised and bilateral lymph node enlargement. A small percentage may also have nonspecific signs, such as fever, anorexia or apathy. This depends on the organs affected, and it is not uncommon to find splenomegaly and liver, mediastinal or bone marrow involvement. About 10–20% of patients course with hypercalcaemia, a common paraneoplastic syndrome.
• Mediastinal: This is characterised by a lymphadenomegaly of mediastinal nodules, which causes compression leading to cough, exercise intolerance and dyspnoea, among others.
• Alimentary or gastrointestinal: May occur as a single mass or diffusely throughout the entire tract. Mainly produces gastrointestinal signs. The spleen and liver may be involved.
• Extranodal: This affects a specific organ; the skin, kidneys, eyes or nervous system.

Diagnosis and treatment

The diagnosis is usually made using immunohistochemical techniques on biopsy samples, but complementary tests are very important to assess the extent of the disease correctly.

The treatment of choice for multicentric lymphoma in dogs is chemotherapy. The possibilities of remission and survival, as well as the costs, duration and side effects of treatment, should be discussed with the owner. Approximately 90% of sick animals achieve remission.

Predictors of long-term survival

A retrospective study⁽¹⁾ was conducted in 127 dogs with high-grade multicentric lymphoma treated with chemotherapy in four veterinary hospitals between 2000 and 2009. The study compared a multitude of data, such as the origin, history, haematological parameters, tumour characteristics, treatment and prognosis, in an attempt to determine which factors are key to the animal surviving the lymphoma.

It was observed that 10% of the dogs survived for over 2 years. Survivors who lived for more than 2 years were 4% (3 years), 3% (4 years) and 1% (5 years). At the time of diagnosis, eleven of the thirteen long-term survivors shared the following characteristics:

• Body weight greater than or equal to 10 kg
• Haematocrit greater than or equal to 35%
• Absence of ionised hypercalcaemia
• Centroblastic lymphoma (with a high degree of malignancy, and constituted mainly of centroblasts)
• Immunophenotype B
• No bone marrow involvement.
• Lymphoma stage I to IV: no corticosteroids had been used.

Another interesting fact observed is that six of the long-term survivors died during the study. Four of those six dogs died from other cancers, three of which were osteosarcomas.

You can assess the body condition of dogs using the Body Condition Score Poster for Dogs

Thus, we can deduce that the absence of the combination of the aforementioned factors can help us predict death beyond 2 years.

(1)   Marconato L, et al. Predictores de supervivencia a largo plazo en perros con linfoma multicéntrico de alto grado. J Am Vet Med Assoc 2011; 238(4):480-485.