Lymphoma in Dogs
WHAT IS LYMPHOMA IN DOGS
Lymphoma is an umbrella term for a range of cancers that affect the lymphocytes, cells which form part of the immune system involved in fighting disease and infection. As lymphocytes travel around the body within the lymphatic system, this form of cancer can be widespread.
HOW IS LYMPHOMA IN DOGS DIAGNOSED?
Most cases of lymphoma can be diagnosed by fine needle biopsy. This can be performed conscious or under a mild sedative, and involves inserting a needle into one of the enlarged lymph nodes and aspirating cells into a syringe ( like an injection in reverse ). The cells are then sprayed onto microscopic slides to be assessed by a pathologist.
In a few cases, a surgical biopsy of a lymph node may be necessary to make a full diagnosis. This is performed under anaesthetic. Solitary and suspected cutaneous lymphomas will be diagnosed similarly.
Chest x-rays and detailed abdominal ultrasound are recommended for assessment of internal lymph node enlargement and organ involvement, and in some cases bone marrow biopsy may also be advised if symptoms or test results suggest that the bone marrow is affected.
Routine blood tests are performed to check haematology ( red and white cells, looking for signs of anaemia or problems with the immune system, and also quantifying platelet numbers, the tiny cell fragments that form an important part of the blood clotting mechanism ) and biochemistry ( looking at organ function ). This is not only important as part of the diagnostic work up of a patient, but forms a vital pre- treatment baseline for future monitoring.
The most common sign of lymphoma is an enlargement of one or more of the peripheral lymph nodes ( or glands ) so that they are readily palpable, or even visible. The peripheral lymph nodes are submandibular ( either side of the throat ), prescapular ( in front of the shoulder blades ), axillary ( in the armpit area ), inguinal ( high up in the groin ) and popliteal ( behind the knees ).
Lymphoma can also spread to the internal lymph nodes within the chest and abdomen, and to organs such as the liver, spleen and bone marrow.
Very occasionally, a solitary mass may develop in the nose. And there is a cutaneous form of lymphoma, appearing as scaling lesions of the skin which do not respond to normal treatments.
Dogs may also develop symptoms such as excessive drinking, weight loss, poor appetite and lethargy.
The most effective treatment for lymphoma is chemotherapy, but it is important to understand the aims and purpose of this, as the way we view cancer treatments in animals is generally different from that in humans.
As our animal patients cannot give their own informed consent, it would be considered unethical to commit them to going through the very aggressive forms of treatment that are offered to people in the hope of it being curative. Rather, our veterinary focus is very much on extending good quality of life. This means that the aim of treatment is achieving remission ( not cure ) with minimal side effects, so chemotherapy tends to be a gentler process using combinations of drugs tailored to each patient.
CHEMOTHERAPY TREATMENT FOR CANINE LYMPHOMA
Chemotherapy is defined as the administration of a drug or drugs which stop or slow down the division and growth of cancer cells.It generally involves regular health checks and blood tests ( to monitor the level of immunosuppression ), sometimes urine tests, and weight checks for accurate calculation of doses.
There are a number of different drugs and protocols. Protocol selection will be dictated by the type of lymphoma, how unwell the patient is, any concurrent medical conditions, practical considerations for the owner, and even patient temperament. Quality of life is of paramount importance.
Most protocols involve daily or alternate day dosing with oral tablets plus either injections under the skin or into the vein via a carefully placed catheter every 1-3 weeks. Most will be continued for 6 months, then stopped if the patient is in remission.
If the patient then relapses, the same protocol may be repeated, or a ‘rescue’ treatment instituted
Chemotherapy is not the right option for every dog or owner. This may be for a variety of practical or financial reasons. Or a protocol may be stopped because of poor response or the development of unacceptable side effects.
In such patients, the use of steroids alone is generally highly recommended as a form of palliative care. Steroids often feature as part of a full protocol, but can be used as the sole treatment, and provide a very useful compromise between no treatment and full chemotherapy.
Steroids do not work for all patients, and it is advisable to have made a very definite decision about whether or not to give chemotherapy before giving them as, once started, steroids alone render any chemotherapeutic drugs added in at a later stage less effective.
However, they do have the advantage of being well tolerated by most patients, and are relatively inexpensive.
WHAT ARE THE SIDE EFFECTS OF TREATMENT?
Most chemotherapy drugs work by damaging rapidly dividing cells. While this obviously targets cancer cells, it can also affect normal cells in the intestines, hair follicles and bone marrow ( which is involved in producing blood cells ).
Significant hair loss does not tend to be a problem in our animal patients. Some pets may lose their whiskers, and some breeds of dog eg poodles and schnauzers are more susceptible to fur loss. Fur will regrow after the end of treatment.
Appetite can be reduced, and diarrhoea or vomiting may develop rarely.
Probably the greatest concern on many protocols is depression of the immune system, hence blood tests will be checked prior to administration of any injections. Drug doses, type or frequency may be altered in light of concerns about side effects, and other medications can be given to alleviate symptoms.
Other side effects may be seen with specific drugs eg increased appetite, thirst and urination with steroids, irritation of the bladder causing cystitis type symptoms with cyclophosphamide, or the potential for damage to the heart muscle with Epirubicin.
Unfortunately it is impossible to predict an individual’s susceptibility to side effects, but they are generally less common and much less severe than those associated with human chemotherapy.
Depending on the drugs used, owners will receive advice on the handling of any waste products ( urine, faeces, vomit etc ) that may contain breakdown products of the treatment.
WHAT IS THE PROGNOSIS FOR DOGS WITH LYMPHOMA?
Prognosis varies greatly between individual patients, but the average life expectancy post diagnosis without any treatment at all is 1-3 months.
With steroid therapy alone, life expectancy increases to 3-6 months.
Most chemotherapy protocols will improve survival times to 6-12 months, sometimes longer.
However, the length of remission is affected by multiple factors such as the primary location of the lymphoma and the extent of spread through the body, how unwell the patient was at time of diagnosis, and the type and grade of lymphoma ( low grade lymphoma, although slower in progression, may respond poorly to treatment because the cancer cells are dividing less frequently so show poor uptake of drugs. Whereas a high grade lymphoma, although much more aggressive in its behaviour, may respond extremely quickly as the rapidly dividing cells take up high concentrations of chemotherapeutic agents ).
The sole aim of treatment is to achieve a period of remission during which the symptoms of lymphoma are absent ( the disease is still present but not clinically detectable ) and the patient has a normal quality of life - eating, drinking, exercising and generally behaving as normal. Any side effects of the treatment should be minimal and managed so as not to impact negatively on quality of life.
However, all periods of remission will come to an end as the remaining cancer cells develop resistance to treatment, and symptoms such as lymph node enlargement reappear. If relapse cannot be controlled with restarting chemotherapy or changing to a different ‘rescue ‘ protocol, then sadly euthanasia must be considered at this stage. For many patients, this decision will have been discussed with the vet well in advance as a vital part of the overall quality of life assessment. Committing to treatment to achieve good quality of life in remission also means being able to make the humane and compassionate decision to allow the pet a peaceful and dignified death when uncontrollable relapse of lymphoma occurs.