Most forms of lymphoma are multicentric and therefore demand a systemic approach. This is why chemotherapy is the preferred treatment option for most forms of lymphoma, as chemotherapeutics reach cancer cells via the bloodstream. Chemotherapy is very well tolerated by companion animals. If the lymphoma is located in 1 spot, local removal via surgery or radiotherapy is the preferred treatment option.
Combination chemotherapy is most frequently used for the treatment of a malignant form of lymphoma. This consists of different kinds of chemotherapeutics that are sequentially administered during the course of the treatment. How long the treatment is maintained and which chemotherapeutics are exactly used, depend on the (sub)stage of the forms of lymphoma, the presence or absence of paraneoplastic disease, the general state of the dog, the comfort of the dog before and just after treatment vs the chance of response to treatment, side effects of the treatment and of course the time and amounts the owners can invest (some protocols take up to 10 months with weekly treatments, others 15 weeks with treatment every 3 weeks). Combination chemotherapy is generally preferred to chemotherapy with only one kind of chemotherapeutic.
Remission (the disappearance of the tumor) occurs in 89 to 90% of dogs after combination chemotherapy. The median survival time is 10 to 12 months. After 2 years, 20-25% of dogs treated with combination chemotherapy are still alive.
The cost of combination chemotherapy depends on the chemotherapeutic used, the size of the animal, the frequency of administration and (lab) monitoring. Before each chemotherapeutic treatment, a blood examination should be done to evaluate whether the levels of certain blood cells are sufficiently high to allow the administration of a new treatment session. If the levels are too low, one should wait 5 to 7 days before checking these again. If there’s a form of lymphoma present in the bone marrow, these blood levels are more difficult to interpret.
Although the tumors will initially disappear in many dogs, most will relapse (generally within 1 year). The cause is difficult to find out and can be e.g be related to the fact that the dog has initially been treated with prednisolone, the administered doses have been adapted to what the dog can tolerate, or an insufficiently high concentration of the chemotherapeutic ends up in the tumor, or possibly because the cancer cells became more resistant to the chemotherapeutics.
When a dog relapses, it’s necessary to repeat the treatment or to start up another treatment protocol with substances the dog has not received before (rescue protocol).
In case of a high-grade form of lymphoma, 1 chemotherapeutic -besides doxorubicin and lomustin (CCNU)- will typically not lead to a durable remission compared to the standard combination protocols. With certain types of low-grade lymphoma, the use of only chlorambucil (Leukeran®) possibly combined with prednisolone, can lead to a long survival time.
Enzyme therapy such as PEG asparaginase (Oncaspar®) offers an alternative to those who do not want to start with chemotherapy for the treatment of malignant lymphoma forms or leukemia. It is also used in conjunction with chemotherapy. This enzyme breaks down nutrients (the amino acid asparagine) for the cancer cell, preventing it from dividing. With this therapy one does not achieve a cure, but rather a suppression of the disease.
This drug is quite safe for the dog and the waste products from PEG asparaginase are less harmful than those from chemotherapy. As a result, owners do not have to take precautions with feces / urine / saliva and pets can still be treated if they are in a family with children or pregnant women and chemotherapy is not recommended. There is no need for IVs and bone marrow suppression rarely occurs.
The main side effect is 1-2 days of diarrhea and sometimes poor appetite, but this usually only occurs when the lymph nodes respond very well to treatment and shrink very quickly. Hypersensitivity reactions are rare and can manifest as itching, redness, bumps, scabs or muscle pain.
The therapy consists of 1 injection into the muscles (or an intravenous infusion) every 2-3 weeks and if successful, the intermediate period is extended.
Oncaspar® is an expensive medicine with a limited shelf life.
Much research is done on immunotherapeutic alternatives for dogs with a malignant form of lymphoma.
The antibody Rituximab is used in humans, but has no effect on canine lymphoma. Multiple studies have been performed on vaccines against lymphoma. The results are promising, but convincing vaccines have not reached the market yet. At this time, no immunotherapeutic treatments have been registered yet to be used against lymphoma in dogs.
Administration of prednisolon can be considered as palliative option. The use of steroids prior the chemotherapy can negatively affect the chemotherapy.
Surgery can be appropriate when it entails a single lymph node (phase I) or when it’s a single tumor not localized in the lymph nodes. E.g. in case of a form of lymphoma is present in the eye or a solitary tumor in the digestive system, its surgical removal has led to encouraging results.
Radiotherapy can be indicated when only a single lymph node is involved (phase I) or a solitary form of lymphoma not localized in the lymph nodes. An example would be the mucous membranes of the nose. It can also be used for local palliative care (pain relief). Forms of lymphoma located in the central nervous system can be irradiated, but this leads in general to a low response of short duration (a few weeks to months).
Radiotherapy of the whole body is a possible option in humans, if followed by bone marrow or stem cell transplantation. Bone marrow transplants as described in humans, is not a standard treatment option for companion animals in Europe. After consultation with a radiotherapist and oncologist, it can be decided to irradiate the entire body of the dog, it depends on the case. Radiotherapy can also be used in between chemotherapeutic cycles or after chemotherapy.