Lymphocytes are white blood cells, that is to say small elements (cells) that intervene to protect the body against certain infections: these lymphocytes are part of the immune system. They are found everywhere in the body, in the blood but also in all the immune organs constituting reserves: the ganglia (also called lymphatic nodes), the liver, the spleen, the thymus. These lymphocytes can also be found in other tissues: the digestive tract, the skin …
A lymphoma in dogs is a malignant cell proliferation of these lymphocytes in one or more organs making up the lymphatic system in the broad sense. It is therefore a cancer that can take different forms, especially since there are also several types of lymphocytes (B and T in particular).
Statistics show a clear racial predisposition in Boxers and Golden Retriever, a little less clear in Saint Bernard, German Shepherd, Beauceron. Lymphoma usually affects middle-aged animals, between 5 and 10 years old. However, animals of all ages and breeds can be affected.
Classification of lymphomas
It is not correct to speak of lymphoma but rather of lymphoma. In fact, the behavior of lymphomas is not the same in one dog or another. It depends in particular:
- the type of lymphoma: we speak, for example, of B lymphoma or T lymphoma depending on the type of lymphocytes which is multiplying.
- the rate of multiplication and proliferation of lymphoma: this is referred to as low-grade lymphoma of malignancy (slow multiplication) or high-grade (rapid multiplication)
- localization: lymphoma, ganglionic, digestive, pulmonary, cutaneous, nervous, nasal …
- dissemination: damage to one organ, several or generalization.
- possible blood changes associated with these lymphomas: evolution to a leukemic state or not, presence of too much calcium in the blood (often encountered during lymphoma and pejorative criterion of evolution), presence of anemia
In his approach, your veterinarian must evaluate all of these criteria to give the most precise possible prognosis and offer you the most suitable treatment possible.
In practice, it is possible to present lymphomas according to their primary anatomical location.
Multicentric lymph node lymphoma
It is the most frequent form, more than 80% of reported cases. One then several lymph nodes grow gradually due to the multiplication of lymphocytes. It is not uncommon to discover, by chance, that a lymph node is enlarged without other symptoms at first. But, usually, the general condition is altered: loss of appetite, weight loss, fatigue, possibly fever. This lymph node involvement can extend to the liver, spleen, and bone marrow most often. In about 30% of cases, it is possible to demonstrate paraneoplastic hypercalcemia, that is to say an increase in the concentration of calcium in the blood at the origin of an increased intake of drink.
It accounts for about 5% of lymphoma cases. The tumor can manifest itself in two ways:
either by the presence of a nodule or of a focal mass, localized, at the level of the wall of the digestive tract which can cause partial or total digestive obstruction.
or by the presence of a diffuse infiltration within the wall of the digestive tract, causing thickening of the latter.
These damage can spread to the drainage nodes in the abdomen.
The most common symptoms are: loss of appetite, diarrhea, vomiting(possibly with traces of blood), weight loss.
The mediastinum is the part of the thorax located between the two lungs and containing, among other things, the heart, esophagus and trachea. Many lymph nodes and the thymus are there and can develop lymphoma. The resulting respiratory symptoms can be varied: cough, respiratory discordance, rapid breathing, open mouth breathing, etc. Digestive symptoms (vomiting, regurgitation) may also be present. These disorders are secondary to the presence of a lump or effusion (fluid) in the chest.
Cases of pulmonary lymphoma, with similar symptoms, are described but rarer.
Lymphomas from other locations in dogs
Skin or subcutaneous nodules associated with intense itching (pruritus), erythema (pinkish red skin), hair loss, flaking (dandruff) are present.
Lymphomas of the eye and nervous system
The eye may be lymphomatous: in this case, it may have a larger volume, become more cloudy or take on a hemorrhagic appearance. The brain or the spinal cord can be infiltrated by cancerous lymphocytes: neurological disorders are then present (loss of vigilance, convulsions, behavioral disorders, loss of balance, paralysis, etc.).
Lymphomas of the abdominal organs
Both the liver and the spleen can be affected in isolation or be affected secondarily. One or more kidneys may be affected by lymphoma and, like the other abdominal organs, present a clinical picture related to their progressive failure.
Lymphomas of the nasal cavities
Infiltration of the dog’s nasal cavities by lymphomatous tumor cells is possible. It can cause respiratory discomfort, sneezing, nasal discharge (purulent, hemorrhagic, etc.). Deformation of the nasal cavities may even be present in some cases.
Diagnosis and assessment of extension
As mentioned previously, the veterinarian must carry out investigations in order to:
- determine the presence of lymphoma
- to know his behavior (aggressive or not)
- to seek its extension to other organs or not (we speak of “extension assessment”)
- to know the blood complications.
For this, additional examinations must be carried out:
- puncture or biopsy of suspected organs
- x-ray, ultrasound or even CT or endoscopic examination are necessary in order to carry out an extension assessment
- a blood test is essential.
These examinations are painless; it may sometimes be necessary to perform some of these tests under anesthesia.
Lymphoma treatments and its prognosis
Most lymphomas require medical treatment in the form of chemotherapy. These are oral or intravenous treatments: different protocols exist. Their effectiveness, their toxicity, their cost will be detailed to you by your veterinarian.
In certain cases (damage to an organ – rate, eye for example -, during digestive obstruction, etc.), surgical management must be proposed as a first-line treatment: it will be supplemented, most often, by adjuvant chemotherapy.
Finally, in other cases, radiotherapy is possible (tumor of the nasal cavities for example).
Lymphoma in dogs remains a rather poor prognosis because half of the dogs under treatment die within a year of detecting this cancer. Nevertheless, the prognosis depends a lot on the extent of the tumor, its type, the therapeutic protocol envisaged …
In some cases, palliative treatments may be offered.