Robyn Elmslie, DVM DACVIM (Oncology)
Veterinary Cancer Specialists at VRCC
Lymphoma is a lymph node cancer in dogs, similar to non-Hodgkin
lymphoma in people, and affects approximately 15% of dogs with
cancer. It is rapidly progressive without treatment and very
difficult to cure. Chemotherapy continues to be the treatment
of choice for dogs with lymphoma. The most commonly used
chemotherapy protocols consist of a combination of chemotherapy
drugs, most of which are given by injection. The goal is to combine
chemotherapy drugs with different mechanisms of action for killing
cancer cells, which in turn increases the probability of inducing a
complete remission and long-term survival. At the same time,
combination chemotherapy protocols increase the time it takes for
the cancer cells to become resistant to treatment. Â Many
variations of these multidrug protocols exist but the most widely
used is a combination of doxorubicin, vincristine, prednisone and
cyclophosphamide, known as CHOP. Treatment with CHOP has been
reported to result in median remission times of 174 to 204 days
 (Hosoya et al JVIM 2007; Simon et al JAVMA 2008) and to
result in median survival times of 275-322 days. While some CHOP
treated lymphoma patients have very short remission and survival
times, 26% of dogs treated with CHOP live more than 2 years (Simon
et al JAVMA 2008).Â
Much research effort has been devoted to trying to understand
why some patients with lymphoma respond so well to treatment,
whereas others respond so poorly. Â Several factors have been
identified that negatively impact outcomes in dogs with lymphoma
treated with chemotherapy. One of the most important factors
is the type of lymphocyte from which the lymphoma arises (Marconato
et al. JAVMA 2011). Lymphomas are broadly categorized into
B-cell and T-cell lymphoma. It is generally accepted and
widely reported in the literature that dogs with T cell lymphoma do
much more poorly than dogs with B cell lymphoma, when treated with
the CHOP protocol. Beaver et al., first reported in 2009
(Veterinary Cancer Society Conference, Oct 2009), that one of the
key drugs in the CHOP protocol, doxorubicin, was poorly effective
for the treatment of T-cell lymphoma in dogs, and therefore may
explain why dogs with T cell lymphoma have been reported to have
short remission and survival times when treated with
CHOP.  In their study, Beaver et al. treated 29 dogs with
B-cell lymphoma and 12 dogs with T-cell lymphoma with doxorubicin
as the first chemotherapy drug, to assess response to
treatment. Complete remission was achieved in 86.2% of dogs
with B-cell lymphoma after just one treatment with doxorubicin
whereas only 17% (2/12) of dogs with T-cell lymphoma achieved a
complete remission after one treatment of doxorubicin. In a
standard CHOP protocol, patients are treated with a different
chemotherapy drug each week for the first 4 weeks of the
protocol. Doxorubicin is typically given on the third or 4
week of the protocol. By this time, most patients with
lymphoma, regardless of whether they have T or B cell lymphoma, are
already in remission and therefore the actual benefit of
doxorubicin in the CHOP protocol cannot be directly
measured.Â
Does this mean that dogs with T cell lymphoma should never be
treated with doxorubicin or CHOP?Â
Rebhun et al (VCO 2011) recently reported a median remission of
104 days and a median survival time of 235 days in 24 dogs with T
cell lymphoma treated with CHOP. In this study, Rebhun
reported that 14% of patients lived one year and 5 % of patients
lived 2 years. Brodsky et al (VCS 2009) reported more favorable
results for patients with T cell lymphoma in a study of 50 dogs
treated with an alternative protocol known as L-MOPP. In this
study, 25% of dogs with T cell lymphoma were reported to survive
more than 2.5 years.Â
There is not currently consensus in the Veterinary Oncology
community regarding the best chemotherapy protocol for the
treatment of patients with T cell lymphoma. At Veterinary
Cancer Specialists at VRCC, we continue to treat each patient as an
individual. There is not one approach that is best for every
patient. Many factors must be considered in making treatment
recommendations. As new research information becomes
available, we incorporate that knowledge into our recommendations
for our patients and their owners. To learn more about Dr.
Elmslie, the Oncology Team and cancer treatments, please visit
www.vetcancerspecialists.com and www.vrcc.com. Â
