Page 1352 - Clinical Small Animal Internal Medicine

1290 Section 11 Oncologic Disease

where chemotherapy is the primary treatment recom- been shown to result in longer survival times compared
VetBooks.ir mendation. Surgery is only recommended in patients to other treatments. Therefore, the use of tyrosine kinase
inhibitors in dogs with nonresectable, recurrent or met-
with intestinal lymphoma when there is evidence of
intestinal perforation or obstruction. It is recommended
express KIT/CD117. Activating mutations have been
that 5–6 cm of normal intestine on either side of the astatic GISTs is reasonable as GISTs in both species
tumor be excised. For animals with colonic tumors, sub- found involving c‐kit in both dogs and humans and are
total colectomy may be necessary. One study found that thought to be the driving force for GIST development.
cats that had subtotal colectomy for colonic adenocarci- There are two oral tyrosine kinase inhibitors in veteri-
noma had improved survival times over cats that had just nary medicine, toceranib phosphate (Palladia™) and
mass resection or mass biopsy. The authors of the study masitinib mesylate (Masi). Only Palladia, is approved for
do not suggest that every cat with a colonic mass should use in dogs with mast cell tumors in the USA. Regardless,
receive subtotal colectomy but wide surgical margins are both inhibit KIT but their use in dogs with GISTs has yet
recommended. Biopsy of the local lymph nodes, liver, to be investigated.
and any other abnormal‐appearing abdominal organ is Chemotherapy is the primary treatment for intestinal
recommended to assess for metastasis. For dogs and cats lymphoma in dogs due to the multifocal or diffuse nature
with rectal tumors, a transanal pull‐through procedure of the disease. Although CHOP (cyclophosphamide,
has been found to be effective. A combined abdominal‐ doxorubicin, vincristine, prednisone)‐based protocols
transanal approach may be necessary for tumors located are considered the standard of care for dogs with multi-
at the cranial extent of the rectum extending to the centric lymphoma, due to the poor response of dogs
descending colon. with intestinal lymphoma other alkylating agent‐based
The benefit of postoperative chemotherapy is unknown protocols, including MOPP (mechlorethamine HCL,
for dogs with small intestinal adenocarcinoma. However, vincristine sulfate, procarbazine, prednisone), lomustine
due to the moderate to high metastatic rate, the inclu- or DTIC/lomustine, may provide improved survival
sion of adjuvant chemotherapy with doxorubicin‐based times.
protocols would be logical. Approximately 50% of intes- In cats with intestinal lymphoma, the treatment proto-
tinal adenocarcinomas in dogs expres COX‐2. The prod- col varies depending on whether they have low‐grade
ucts of the COX‐2 enzyme have been associated with versus intermediate to high‐grade lymphoma. The treat-
protumorigenic effects such as angiogenesis, cell prolif- ment of low‐grade lymphoma consists of the administra-
eration, and inhibition of apoptosis. Therefore, the tion of prednisolone and chlorambucil. One study
author recommends including NSAIDs in the treatment evaluating cats with low‐grade intestinal lymphoma
protocol for dogs with intestinal adenocarcinomas as found that 78% were cobalamin (vitamin B12) deficient,
they have antineoplastic activity that may help improve thus requiring cobalamin supplementation. Cobalamin
response and survival. The metastatic rate of small is absorbed exclusively in the ileum, complexed with
intestinal carcinoma in cats is also high. Postoperative intrinsic factor. Low cobalamin is associated with meta-
chemotherapy is recommended to help control metasta- bolic derangements and low concentrations of several
sis and to prolong survival. A study evaluating cats with amino acids. Intermediate to high‐grade lymphomare-
large intestinal carcinoma did show a survival advantage quires more aggressive therapy. The best response,
for those that received doxorubicin chemotherapy post- remission duration, and survival time is generally
operatively. Whether this chemotherapy protocol is ben- achieved with CHOP‐based chemotherapy protocols.
eficial in cats with small intestinal carcinoma has yet to Eventually, most cats relapse and/or develop resistant
be determined but it is a logical choice for postoperative disease. If relapsing after completing their initial CHOP
therapy. chemotherapy protocol, it can be restarted. The second
As with small intestinal adenocarcinoma, the use of remission is generally about half the duration of the first.
postoperative chemotherapy in dogs with small intesti- Once they fail CHOP, rescue chemotherapy can be
nal leiomyosarcoma has yet to be investigated in a rand- attempted. The most successful rescue chemotherapy
omized clinical trial. However, based on the moderate to protocols include MOPP and lomustine.
high metastatic rate (16–50%), chemotherapy should be If a solitary mass is present and there is no evidence of
included in the treatment protocol. Surgical removal metastatic disease, surgical removal can be attempted in
alone results in prolonged survival times (over three cats with intestinal mast cell tumors. Due to the high rate
years) for dogs with GISTs. However, for those few cases of disseminated disease with intestinal mast cell tumors,
in which GISTs are nonresectable or metastatic, adju- postoperative chemotherapy is recommended based on
vant treatment with tyrosine kinase inhibitors may be the likelihood of residual micrometastasis. If the intesti-
useful. In humans with nonresectable or metastatic nal mast cell tumor is not resectable or metastatic dis-
GISTs, treatment with tyrosine kinase inhibitors has ease is present at the time of diagnosis, chemotherapy