Lymphoma is one of the most common malignancies to affect dogs
Lymphoma is one of the most common malignancies to affect dogs, having an estimated annual incidence of approximately 25 per 100,000 dogs. The occurrence of lymphoma increases with age, and has a median age of onset around seven years old. Strong predispositions are known for many breeds with Golden Retrievers, Boxers, West Highland Terriers being particularly prone to the disease.
Typical presenting signs of canine lymphoma:
- Vomiting and Diarrhoea
- Weight Loss
- Loss of Appetite
- Lethargy/Loss of Stamina
Definitive diagnosis requires cytological examination of tissue from fine needle aspirate (FNA), or, preferably histological classification of a biopsy collected from the affected tissue. Once diagnosed, patients generally respond rapidly to chemotherapy, with peripheral lymphadenopathy being visibly reduced within seven days:
A range of chemotherapy protocols are available from single agent therapies to multidrug treatments. Each have been shown to have different median survival times (MST):
- Untreated MST= 4-6 weeks
- Prednisone monotherapy MST= 2 months
- Doxorubicine monotherapy MST= 6-8 months
- CHOP based protocols MST= 10-12 months and 20-25% of the patients will be alive at 2 years
Regardless of initial therapy, the disease invariably recurs and second round treatment is considered to be less effective due to development of drug resistance.
At the first recurrence, re-induction therapy is recommended. This involves reintroducing the original induction protocol. However, the likelihood of response and duration of a second remission are approximately half that achieved by the initial protocol. When re-induction fails, rescue agents which were not included in the original protocol may be used. These include single agents such as lomustine, mitoxantrone or actinomycin D and also combination therapies such as MOPP (methclorethamine, vincristine, procarbazine and prednisolone). Response rates are reported to be in the range of 40 to 50%, but median survival times are currently only about 2 months.
Due to the high risk of recurrence and consequent problems, close monitoring of dogs undergoing chemotherapy is important.
The same is true for dogs that have entered remission and ceased treatment. It is believed that re-induction or rescue therapy may be more effective when recurrence is detected in its early stages. Monitoring for disease remission/recurrence is usually performed by palpation of peripheral lymph nodes. However, this can be a very subjective procedure which is only capable of detecting gross changes in peripheral lymph nodes.