Canine Lymphomas

What is a lymphoma?

Lymphomas are cancers of the lymphocytes, a type of immune cell. In dogs, they generally arise from the lymph nodes but other organs can also be involved. As immune cells are made to travel within the body to fight against infection, lymphomas often inherit from this trait and can easily spread throughout the body.

What are the different types of lymphomas?

The human WHO lymphoma classification has been adapted to dogs and there are currently more than 30 different subtypes of lymphomas that have been characterised. One way to divide these subtypes is by typing the lymphoma cells between the T-cell lymphomas and the B-cell lymphomas. We can classify lymphomas based on their organ of origin. Most of lymphomas originate from the lymph nodes, which are rounded and firm structures we can feel under the skin. Less commonly, lymphomas can start from within the chest, the bowels, the skin …  Some lymphomas will progress very slowly (indolent / low grade), whilst the majority will progress quickly (aggressive / high grade). Oncologists need to know the organ of origin, the clinical behaviour and grade, as well as type and subtype of the lymphoma to get a better understanding of each individual case. The most common subtype is the intermediate-high grade diffuse large B-cell multicentric lymphoma, representing about half of all lymphomas in dogs.

How can I tell if my dog has lymphoma?

This depends on where the lymphoma is. Most lymphomas in dogs start from the lymph nodes and owners often report “new lumps”. Dogs’ lymph nodes can be felt under the jaw (mandibular lymph nodes), between the shoulders and the neck (prescapular lymph nodes), and behind the knees (popliteal lymph nodes). More than a quarter of dogs diagnosed with lymphoma are clinically well but are presented because of these new lumps that may be detected by owners. The other dogs are presented with various symptoms, often including decreased appetite and lethargy. Depending on the nature and origin of the lymphoma, some dogs may have diarrhoea, increased breathing effort or increased drinking. These symptoms remain vague and non-specific.

What causes lymphoma?

Generally speaking, we do not know exactly what causes lymphoma, and it is likely that genetic and environmental factors play a role. Some breeds may be predisposed to certain types and subtypes of lymphomas. Some studies have also suggested that exposure to some chemicals may also increase the risk of developing lymphoma.

How are lymphomas diagnosed?

Most lymphomas are usually diagnosed with fine-needle aspirate cytology. We can use a needle similar to the ones for vaccines, and obtained some cells from an enlarged lymph node. This test is quick and does not usually require any sedation. This sample can also be sent for flow cytometry, which is a more advanced test that can help better characterise the lymphoma, and in particular determining if it is a B-type or a T-type. Some biopsies may also be performed, especially to diagnose more unusual lymphomas (e.g. low grade lymphomas of the lymph nodes), or lymphomas originating from other locations such as the skin. 

Other tests can be performed to stage lymphomas and assess where it has spread. These may include blood tests (complete blood count and blood smear), bone marrow aspirate, abdominal ultrasound, thoracic radiographs, liver and spleen fine-needle aspirates. 

How are lymphomas treated?

In rare cases, lymphomas may still be localised and can be treated with some local therapies such as surgery and/or radiation therapy. In more than 90% of cases, however, the lymphoma has already spread and some sort of systemic treatment is required. This generally include standard-dose chemotherapy. A chemotherapy protocol with a combination of different drugs is usually preferred as a first-line, in particular a CHOP protocol (including prednisolone, vincristine, cyclophosphamide, and doxorubicin).  Other drugs and chemotherapy protocols are possible. Chemotherapy drugs can be administered on their own or as part of a combination, some are administered intravenously whilst others can be given orally. They can be administered as frequently as once a week, or up to every 3 weeks. Some slowly progressive lymphomas may be treated with other drugs, including low dose oral chemotherapy at home. Our aim is to make sure dogs under treatment have a good quality of life for as long as possible. Our team is particularly invested in improving the management of chemotherapy adverse effects (links QF research? https://www.fitzpatrickreferrals.co.uk/research-centre/chemotherapy%e2%80%90induced-diarrhoea-in-dogs-and-its-management-with-smectite-results-of-a-monocentric-open%e2%80%90label-randomized-clinical-trial/; https://www.fitzpatrickreferrals.co.uk/research-centre/impact-of-pre-chemotherapy-neutrophil-count-on-chemotherapy-administration-and-toxicity-in-dogs-with-lymphoma-treated-with-chop-chemotherapy/; https://www.fitzpatrickreferrals.co.uk/research-centre/evaluation-of-a-0-75-x-10-9-l-absolute-neutrophil-count-cut-off-for-antimicrobial-prophylaxis-in-canine-cancer-chemotherapy-patients/), and improving the design of chemotherapy protocols. We are able to provide a wide variety of treatments, including the novel drug Tanovea® and the autologous vaccine APAVAC®.

What are the prognoses of lymphomas?

Prognoses of lymphomas can vary considerably between anatomical locations, types and subtypes. The average medial survival time for high-grade multicentric lymphomas (the most common form) is about one year with standard of care treatment, and about 20% of dogs are still alive 2 years after diagnosis. Although remission is obtained in > 80-95% dogs, many cases will eventually relapse over time. Some forms of low-grade lymphomas may have much a better prognosis, whilst other aggressive forms may have a worse prognosis. Our medical oncologists would be able to guide you with the information available for your dog.

 

 

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