Outcomes For High-Grade Canine Lymphoma

High-grade canine lymphoma is an aggressive cancer which unfortunately has an average survival of one month without treatment. The response to chemotherapy in most dogs with lymphoma is dramatic with approximately 90% of cancer cells killed with each dose and complete remission rates of 80 to 90%. Unfortunately, most dogs will eventually relapse and succumb to the disease with fewer than 10% of dogs likely to be cured
by chemotherapy alone. Average remission duration is approximately 12 months with chemotherapy.

Over the last 10 or 20 years there have been many efforts to improve the long-term outcome for dogs with high-grade lymphoma but despite many attempts and many studies using variations on available chemotherapy treatments, clinically significant improvements in outcome have not been achieved.

Half Body Irradiation

Half body irradiation (HBI) is an emerging treatment showing great promise when combined with chemotherapy to treat lymphoma in dogs. This treatment makes use of a linear accelerator (which is essentially a very high powered x-ray machine) to expose half of the body to radiation. Lymphoma cells are extremely sensitive to radiation and areas exposed to this dose are likely to experience death of 99% of cancer cells. While irradiating the entire body is possible, the dose required to kill the cancer would also result in the need for a bone marrow transplant. With HBI the front half of the body is irradiated first, followed by the second half two weeks later. This allows the bone marrow cells to migrate between the halves and thus recover without needing bone marrow transplantation. Cancer cells are much less efficient at repopulating in patients showing complete remission and, in addition, between the two doses of HBI we administer a single dose of chemotherapy which kills cancer cells without damaging the bone marrow; this minimises the opportunity for the lymphoma cells to “jump across the body between doses of radiation.

This is a very exciting development in the treatment of lymphoma in dogs and early studies have not only demonstrated increased survival times but most excitingly suggest that the percentage of dogs cured of their lymphoma increases from approximately 10% to approximately 35 to 40%.

In 2020, BVSC and the Australian Animal Cancer Foundation presented the results of the first case controlled prospective study assessing the benefits of half body irradiation in our patients. This study was presented at the European College of Veterinary Internal Medicine on line congress. Our results were even better than those previously published in the USA with 56% of treated dogs still in their first remission at 2 years.

Side-Effects

Side-effects from HBI are not dissimilar to those experienced from chemotherapy, both in terms of severity and frequency. The most common side effects are mild to moderate gastrointestinal signs such as a reduced appetite and mild lethargy for 2 to 7 days after
the second treatment. A small number of dogs show significant reductions in white blood cell counts and clotting cell counts and in most cases these can be managed easily with supportive care. It should also be noted that a portion of dogs will suffer some temporary hair loss (particularly breeds with continuous coat growth such as poodles) and/or a change in coat colour (it may become paler) which may or may not be permanent.

The Protocol

HBI is provided on site at Brisbane Veterinary Specialist Centre and can be provided as an outpatient service. Our recommended protocol is to replace the second round of chemotherapy treatments with the two HBI treatments and a single dose of chemotherapy. An example protocol is provided below; for patients on a different chemotherapy protocol we will be able to advise you on how yours would differ.

Week HBI & Chemotherapy
1 Vincristine
2 Cyclophosphamide
3 Vincristine
4 Doxorubicin
5
6 HBIcr
7 Chemotherapy
8 HBIcd
9
10 Vincristine
11 Cyclophosphamide
12 Vincristine
13 Doxorubicin
14
15 Vincristine
16 Cyclophosphamide
17 Vincristine
18 Doxorubicin